Growth, biomass production and photosynthesis of Cenchrus ciliaris L. under Acacia tortilis (Forssk.) Hayne based silvopastoral systems in semi arid tropics

The growth, biomass production and photosynthesis of Cenchrus ciliaris was studied under the canopies of 17 yr old Acacia tortilis trees in semi arid tropical environment. On an average the full grown canopy of A. tortilis at the spacing of 4 x 4 m allowed 55% of total Photosynthetically Active Radiation (PAR) which in turn increased Relative Humidity (RH) and reduced under canopy temperature to -1.75 degrees C over the open air temperature. C. ciliaris attained higher height under the shade of A. tortilis. The tiller production and leaf area index decreased marginally under the shade of tree canopies as compared to the open grown grasses. C. ciliaris accumulated higher chlorophyll a and b under the shade of tree canopies indicating its shade adaptation potential. The assimilatory functions such as rate of photosynthesis, transpiration, stomatal conductance, photosynthetic water use efficiency (PN/TR) and carboxylation efficiency (PN/CINT) decreased under the tree canopies due to low availability of PAR. The total biomass production in term of fresh and dry weight decreased under the tree canopies. On average of 2 yr C. ciliaris had produced 12.78 t ha(-1) green and 3.72 -t ha(-1) dry biomass under the tree canopies of A. tortilis. The dry matter yield reduced to 38% under the tree canopies over the open grown grasses. The A. tortilis + C. ciliaris maintained higher soil moisture, organic carbon content and available N P K for sustainable biomass production for the longer period. The higher accumulation of crude protein, starch, sugar and nitrogen in leaves and stem of C. ciliaris indicates that this grass species also maintained its quality under A. tortilis based silvopastoral system. The photosynthesis and dry matter accumulation are closely associated with available PAR indicating that for sustainable production of this grass species in the silvopasture systems for longer period about 55% or more PAR is required.     

大气CO2浓度升高对植物光合作用的影响

大气CO2浓度不断升高以及由此带来的温室效应已成为全球变化研究的热点问题之一。CO2作为植物光合作用的底物,其浓度升高必然对植物的光合作用产生影响。大气CO2浓度升高对植物光合作用的影响主要体现在:对不同植物的光合色素含量均有影响,但结果有所差异;短期处理光合速率提高,而长期处理则可能出现光合适应,其适应机理目前尚存在分歧;不同光合类型植物的叶片形态结构有不同的响应结果,叶绿体超微结构也明显变化;生物量和产量提高。此外,CO2浓度升高与其它环境因子相互作用对植物的光合作用也具有重要影响。大气CO2浓度升高条件下对木本植物的研究、在分子水平上的深入研究以及在不同环境下的研究将成为未来研究的主要方向。     

铜胁迫对高丹草和紫花苜蓿生长和光合特性的影响

以高丹草（Sorghum×S.sudanes）和紫花苜蓿（Medicago sativa L.）为试验材料,通过水培试验,研究了不同浓度Cu处理对两种牧草生长及光合特性的影响。试验结果显示,随着Cu处理浓度增加,两种牧草叶、茎、根生物量逐渐下降,并在100μmol.L-1 Cu2＋处理后达到显著水平。Cu胁迫导致两种牧草气孔导度、RuBP羧化酶的最大羧化效率、最大电子传递速率调控的RuBP再生的潜在速率和磷酸丙糖利用中有机磷的释放速率、以及叶绿素质量分数降低,最终导致净光合速率降低。Cu胁迫下,两种牧草二氧化碳饱和点和二氧化碳饱和点净光合速率降低,而二氧化碳补偿点却升高。另外,Cu处理还降低了两种牧草的蒸腾速率和日间呼吸速率。且在光合、蒸腾和呼吸作用参数的变化幅度上高丹草要大于紫花苜蓿。这些结果表明Cu胁迫抑制了两种牧草的生长、光合作用、蒸腾作用和呼吸作用,而且对高丹草的抑制作用要强于紫花苜蓿;Cu胁迫下光合作用的下降不仅与气孔导度的下降相关,而且与光反应和暗反应的受阻有关。这些研究结果可为筛选和培育耐Cu和富集Cu的牧草品种和用牧草修复铜污染水体及土壤提供依据。     

浮尘对冬小麦叶片光合作用及细胞膜透性的影响

我国是浮尘发生频繁的国家。浮尘作为一种灾害性天气不仅直接危害作物,而且通过减少直接辐射,减缓冰雪融化,减少河水流量,改变土壤性质等间接影响作物的生长发育。因此,深入研究浮尘对作物的影响具有重要意义。但目前,国内外的学者主要偏重研究人为粉尘和工业污染物对野生植物及绿化植物的影响,较少关注自然降尘对作物的影响;特别是在长期浮尘胁迫下冬小麦叶片的气孔导度、净光合速率、细胞质膜相对透性等生理指标的变化很少有研究。通过模拟降尘和盆栽试验,研究了拔节期和盛花期的降尘对冬小麦叶片温度（Tleaf）、叶绿素含量（Chl）、游离脯氨酸含量（Pro）、净光合速率（Pn）、气孔导度（Gs）、胞间CO2浓度（Ci）、细胞膜透性的影响（MP）。结果表明,降尘使拔节期和盛花期冬小麦的净光合速率分别下降52%和43.9%,差异均显著（P〈0.05）;降尘还增大细胞膜透性,破坏了冬小麦自身调节系统,使拔节期和盛花期的叶绿素含量分别下降14.4%和20.4%,达到极显著差异（P〈0.01）;降尘还使拔节期叶片的气孔导度下降到对照的26.9%（P〈0.05）,同时叶面温度升高,脯氨酸含量增加38.2%。     

No evidence that chronic nitrogen additions increase photosynthesis in mature sugar maple forests

Atmospheric nitrogen (N) deposition can increase forest growth. Because N deposition commonly increases foliar N concentrations, it is thought that this increase in forest growth is a consequence of enhanced leaf-level photosynthesis. However, tests of this mechanism have been infrequent, and increases in photosynthesis have not been consistently observed in mature forests subject to chronic N deposition. In four mature northern hardwood forests in the north-central United States, chronic N additions (30 kg N ha(-1) yr(-1) as NaNO3 for 14 years) have increased aboveground growth but have not affected canopy leaf biomass or leaf area index. In order to understand the mechanism behind the increases in growth, we hypothesized that the NO3(-) additions increased foliar N concentrations and leaf-level photosynthesis in the dominant species in these forests (sugar maple, Acer saccharum). The NO3(-) additions significantly increased foliar N. However, there was no significant difference between the ambient and +NO3(-) treatments in two seasons (2006-2007) of instantaneous measurements of photosynthesis from either canopy towers or excised branches. In measurements on excised branches, photosynthetic nitrogen use efficiency (micromol CO2 s(-1) g(-1) N) was significantly decreased (-13%) by NO3(-) additions. Furthermore, we found no consistent NO3(-) effect across all sites in either current foliage or leaf litter collected annually throughout the study (1993-2007) and analyzed for delta 13C and delta 18O, isotopes that can be used together to integrate changes in photosynthesis over time. We observed a small but significant NO3(-) effect on the average area and mass of individual leaves from the excised branches, but these differences varied by site and were countered by changes in leaf number. These photosynthesis and leaf area data together suggest that NO3(-) additions have not stimulated photosynthesis. There is no evidence that nutrient deficiencies have developed at these sites, so unlike other studies of photosynthesis in N-saturated forests, we cannot attribute the lack of a stimulation of photosynthesis to nutrient limitations. Rather than increases in C assimilation, the observed increases in aboveground growth at our study sites are more likely due to shifts in C allocation.     

大气CO2体积分数升高对植物N素吸收的影响

从影响植物N素吸收的因素来看，大气CO2体积分数升高条件下植物净光合作用增强，碳同化产物增多，利于改善N素吸收的能量和物质基础：植物根系生长增强，生物量增多且空间分布加大，有利于N素吸收；但土壤有效N供应能力的变化存在增强和减弱两种观点。从植物N素吸收的实际情况来看，大气CO2体积分数升高条件下植物N吸收总量并末增加，植物体内N质量分数普遍降低，某些种类植物N吸收形态也发生了改变。因此要阐明大气CO2体积分数升高对植物N素吸收的影响机制，必须探明土壤有效N供应能力的变化：CO2体积分数升高条件下N矿化作用是否增强，微生物和植物间是否存在对有效N的竞争，此外，CO2体积分数升高条件下植物根系形态特征变化和N素吸收(包括主动和被动吸收)的生理机制及其与环境因素的关系也值得进一步研究。     

Effects of clonal integration on the growth and physiology of Phalaris arundinacea under simulated herbivory北大核心CSCD

In order to investigate the effects of clonal integration on the adaptation of clonal plants to the environmental stress of homogeneous herbivory, we conducted a greenhouse experiment to investigate the ecophysiological response characteristics of Phalaris arundinacea collected from the riparian zone of the Poyang Lake wetland and Le'an River in Jiangxi Province and the effect of clonal integration on this dominant plant under two-months of simulated cyclical homogenous herbivory. Simulated herbivory strength was set at four different levels: no leaf removal (control) and 25%, 50%, and 75% leaf removal. We implemented two methods of clonal integration including no integration, in which the rhizome connection was severed, and integration, in which the rhizome connection was intact. We found that simulated herbivory significantly decreased the number of leaves, total shoot length, number of ramets, and biomass of P. arundinacea (P < 5%), regardless of whether the rhizomes were intact or severed. Ramets with severed rhizome connections (RRC) generally had higher growth indices than those with intact rhizome connections (RIC). Severing rhizomes did not significantly affect the chlorophyll content of P. arundinacea, while RRC under simulated herbivory intensities of 25% and 50% leaf removal had higher chlorophyll a (Chl a), chlorophyll b (Chl b), and total chlorophyll (Chlt) contents than RIC did, and simulated herbivory increased the chlorophyll contents of all ramets. RRC net photosynthesis rate (Pn), stomatal conductance (Gs), intercellular CO2 concentration (Ci), and transpiration rate (Tr) were all higher in RRC than they were in RIC under simulated herbivory intensities of 50% and 75% leaf removal; however, the opposite relationship was observed under a simulated herbivory intensity of 25% leaf removal. Further, simulated herbivory limited the photosynthetic index of P. arundinacea. These effects resulted in an inadequate accumulation of nutrients in the plant. Phalaris arundinacea can adapt to simulated herbivory treatments in terms of growth, but clonal integration cannot improve the growth of P. arundinacea under a homogeneous herbivory treatment. © 2018 Science Press. All rights reserved.     

Long-term CO2 enrichment of a forest ecosystem: implications for forest regeneration and succession.

The composition and successional status of a forest affect carbon storage and net ecosystem productivity, yet it remains unclear whether elevated atmospheric carbon dioxide (CO2) will impact rates and trajectories of forest succession. We examined how CO2 enrichment (+200 microL CO2/L air differential) affects forest succession through growth and survivorship of tree seedlings, as part of the Duke Forest free-air CO2 enrichment (FACE) experiment in North Carolina, USA. We planted 2352 seedlings of 14 species in the low light forest understory and determined effects of elevated CO2 on individual plant growth, survival, and total sample biomass accumulation, an integrator of plant growth and survivorship over time, for six years. We used a hierarchical Bayes framework to accommodate the uncertainty associated with the availability of light and the variability in growth among individual plants. We found that most species did not exhibit strong responses to CO2. Ulmus alata (+21%), Quercus alba (+9.5%), and nitrogen-fixing Robinia pseudoacacia (+230%) exhibited greater mean annual relative growth rates under elevated CO2 than under ambient conditions. The effects of CO2 were small relative to variability within populations; however, some species grew better under low light conditions when exposed to elevated CO2 than they did under ambient conditions. These species include shade-intolerant Liriodendron tulipifera and Liquidambar styraciflua, intermediate-tolerant Quercus velutina, and shade-tolerant Acer barbatum, A. rubrum, Prunus serotina, Ulmus alata, and Cercis canadensis. Contrary to our expectation, shade-intolerant trees did not survive better with CO2 enrichment, and population-scale responses to CO2 were influenced by survival probabilities in low light. CO2 enrichment did not increase rates of sample biomass accumulation for most species, but it did stimulate biomass growth of shade-tolerant taxa, particularly Acer barbatum and Ulmus alata. Our data suggest a small CO2 fertilization effect on tree productivity, and the possibility of reduced carbon accumulation rates relative to today's forests due to changes in species composition.     

大气CO2浓度升高和氮肥施用对三江平原湿地小叶章生物量及根冠比的影响

利用开顶箱薰气室（open—top chamber）试验装置,研究了不施氮（NN）、施常氮（MN,5g·m^2）和施高氮（HN,15g·m^2）3个氮素水平下大气CO2浓度升高对小叶章（Calamagrostis angustifolia）生物量和根冠比的影响。结果表明,大气CO2浓度升高对小叶章生物量的影响因生长期而异。大气CO2浓度升高对小叶章地上生物量的促进作用主要表现在生长前期,拔节期和抽穗期地上生物量较正常大气CO2浓度增加12．42％～22．60％,而腊熟期和成熟期仅增加3．11％～12．97％;大气CO2浓度升高对小叶章地下生物量的促进作用在生长后期表现明显,除拔节期外,小叶章地下生物量增加17．63％～42．20％。小叶章生物量和根冠比对大气CO2浓度的响应与供N水平有关。在HN水平下,大气CO2浓度升高使小叶章生物量和根冠比明显增加,在NN条件下促进作用则不显著。小叶章根冠比明显增加主要是地下生物量显著增长引起的。     

Laser Radiation Can Retard Leaf Senescence of Isatis Indigotica Seedlings Exposed to Elevated UV-B

以菘蓝(Isatis indigotica Fort)幼苗为实验材料,比较研究了He-Ne激光对增强UV-B(辐射强度:10.08kJ·m-2;照射时间8h·d-1;共照射8d)辐射损伤菘蓝叶片衰老的延缓作用.结果表明:与对照相比,UV-B辐射可导致环丁烷嘧啶二聚体(CPD)形成,显著降低蛋白酶、转氨酶、游离氨基酸、可溶性蛋白质含量,同时降低了叶绿素含量、气孔导度、水分利用率和生物量;而菘蓝幼苗经UV-B辐射处理后再用激光辐照(波长:633nm;功率密度:5.23mW·mm-2;束径:1.5mm;照射时间:5min·d-1),叶片中CPD含量显著降低,蛋白酶、转氨酶、游离氨基酸、可溶性蛋白质含量、叶绿素含量、气孔导度、水分利用率和生物量与单独UV-B处理组相比显著提高.上述结果表明激光辐照可以显著延缓UV-B损伤菘蓝叶片的衰老。     

耐氨固氮菌对蔬菜作物生长的促进作用研究

研究并探讨了蔬菜作物在施用耐氨固氮菌后的生长、生理反应及增产的效果和原因。试验结果表明： 施用耐氨固氮菌显著增加了蔬菜苗期生物量、叶面积和叶片的叶绿素含量, 同时还增强了植株的根系活力, 并有明显的增产效果。耐氨固氮菌促进增产的作用不仅与其本身的固氮作用有关, 还可能与其分泌出某些生长刺激物 （ 或激素） 有关。     

Canopy and leaf composition drive patterns of nutrient release from pruning residues in a coffee agroforest

In a coffee agroforest, the crop is cultivated under the shade of fruit-bearing and nitrogen (N)-fixing trees. These trees are periodically pruned to promote flowering and fruiting as well as to make nutrients stored in tree biomass available to plants. We investigated the effect of canopy composition and substrate quality on decomposition rates and patterns of nutrient release from pruning residues in a coffee agroforest located in Costa Rica's Central Valley. Initial phosphorus (P) release was enhanced under a canopy composed solely of N-fixing, Erythrina poeppigiana compared to a mixed canopy of Erythrina and Musa acuminata (banana). Both initial and final N release were similar under the two canopy types. However, after five months of decomposition, a higher proportion of initial N had been released under the single canopy. Although patterns of decomposition and nutrient release were not predicted by initial substrate quality, mass loss in leaf mixtures rates were well predicted by mean mass loss of their component species. This study identifies specific pruning regimes that may regulate N and P release during crucial growth periods, and it suggests that strategic pruning can enhance nutrient availability. For example, during the onset of rapid fruit growth, a two-species mixture may release more P than a three-species mixture. However, by the time of the harvest, the two- and three-species mixtures have released roughly the same amount of N and P. These nutrients do not always follow the same pattern, as N release can be maximized in single-species substrates, while P release is often facilitated in species mixtures. Our study indicates the importance of management practices in mediating patterns of nutrient release. Future research should investigate how canopy composition and farm management can also mediate on-farm nutrient losses.     

Nitrogen uptake, distribution, turnover, and efficiency of use in a CO2-enriched sweetgum forest

The Progressive Nitrogen Limitation (PNL) hypothesis suggests that ecosystems in a CO2-enriched atmosphere will sequester C and N in long-lived biomass and soil organic pools, thereby limiting available N and constraining the continued response of net primary productivity to elevated [CO2]. Here, we present a six-year record of N dynamics of a sweetgum (Liquidambar styraciflua) stand exposed to elevated [CO2] in the free-air CO2 enrichment (FACE) experiment at Oak Ridge, Tennessee, USA. We also evaluate the concept of PNL for this ecosystem from the perspective of N uptake, content, distribution, and turnover, and N-use efficiency. Leaf N content was 11% lower on a leaf mass basis (NM) and 7% lower on a leaf area basis (NA) in CO2-enriched trees. However, there was no effect of [CO2] on total canopy N content. Resorption of N during senescence was not altered by [CO2], so NM of litter, but not total N content, was reduced. The NM of fine roots was not affected, but the total amount of N required for fine-root production increased significantly, reflecting the large stimulation of fine-root production in this stand. Hence, total N requirement of the trees was higher in elevated [CO2], and the increased requirement was met through an increase in N uptake rather than increased retranslocation of stored reserves. Increased N uptake was correlated with increased net primary productivity (NPP). N-use efficiency, however, did not change with CO2 enrichment because increased N productivity was offset by lower mean residence time of N in the trees. None of the measured responses of plant N dynamics in this ecosystem indicated the occurrence of PNL, and the stimulation of NPP by elevated [CO2] was sustained for the first six years of the experiment. Although there are some indications of developing changes in the N economy, the N supply in the soil at this site may be sufficient to meet an increasing demand for available N, especially as the roots of CO2-enriched trees explore deeper in the soil profile.     

开放式空气CO2浓度升高对水稻根系形态的影响

在FACE（free-air carbon dioxide enrichment）技术平台上，采用水培的研究方法，观测了大气CO2浓度升高和两种氮水平下水稻根系形态的变化。结果表明，在水稻各生育期，CO2浓度升高都极显著增加了根干质量，且主要增加于根粗为2．0～2．5mm／n的部位。根系形态的各项指标均对高CO2浓度有积极的响应，在抽穗期尤为明显；N处理的差异很明显，低氮条件下根系表现为根长、根尖数和根表面积增加，常氮条件下根粗和发根数增加。各生育期的根冠比在高CO2浓度下极显著增加，尤其在LN处理下。水稻从分蘖期到抽穗期，因地上部分的增幅大，根冠比表现为逐渐降低的趋势。     

Effects of fertilization and elevated CO<Subscript>2</Subscript> on larval food and butterfly nectar amino acid preference in<Emphasis Type="Italic"> Coenonympha pamphilus</Emphasis> L.

The effects of larval diet on the nutritional preferences of butterflies has rarely been examined. This study investigates whether alterations in the larval diet result in changes in adult preferences for nectar amino acids. Larvae of Coenonympha pamphilus were raised on fertilized or unfertilized Festuca rubra, grown under ambient (350 ppm) or elevated (750 ppm) atmospheric CO ₂environments. Fertilization led to marked increases in leaf nitrogen concentration. In plants grown under elevated CO ₂conditions, leaf water and nitrogen concentrations were significantly lower, and the C/N-ratio increased significantly. Fertilization of the host plant shortened the development time of C. pamphilus larvae, and pupal weight increased. In contrast, larvae of C. pamphilus developed significantly slower on F. rubra grown under elevated CO ₂, but adult emergence weight was not affected by CO ₂treatment of the plant. C. pamphilus females showed a clear preference for nectar mimics containing amino acids, whereas males, regardless of treatment, either preferred the nectar mimic void of amino acids or showed no preference for the different solutions. Female butterflies raised on fertilized plants showed a significant decline in their preference for nectar mimics containing amino acids. A slight, but not significant, trend towards increased nectar amino acid preference was found in females raised on plants grown under elevated CO ₂. We clearly demonstrate that alterations in larval host quality led to changes in butterfly nectar preferences. The ability of the butterfly to either rely less on nectar uptake or compensate for poor larval conditions represents a trade-off between larval and adult butterfly feeding.     

盐胁迫对油菜幼苗生长和光合特征的影响

采用盆栽砂培试验,研究了不同浓度(0、50、100、200、300mmol·L-1)NaCl胁迫10和30d对油菜(Brassica napus)幼苗干质量、叶绿素(Chl)含量、净光合速率(Pn)、气孔导度(Gs)、细胞间CO2浓度(xi)、蒸腾速率(Rt)、水分利用效率(Ew,u)和气孔限制值(Ls)等的影响.结果表明,在NaCl胁迫下,油菜幼苗植株干质量显著降低,长期高盐胁迫下油菜干质量降低更显著;随NaCl浓度的增加,Chl含量、Chl a/Chl b比值均呈先升高后降低的变化趋势,处理10d,Chl含量、Chl a/Chl b比值在NaCl浓度为200mmol·L-1条件下达最大值,处理30d,在NaCl浓度为100mmol·L-1条件下达最大值.在50～100mmol·L-1NaCl胁迫下,油菜叶片的Pn、xi和Ls所受影响均很小;高盐胁迫下,其Pn、Gs、xi和Rt均显著下降,而Ew,u和Ls则显著上升.相关分析显示,植株干质量与Chl含量、Chl a/Chl b比值间无相关性,与Na+、Cl-含量,Ew,u和Ls间呈显著负相关(P＜0.01),与根冠比,K+、Ca2+含量,K+/Na+、Ca2+/Na+比值,K+与Na+的选择性比率[S(K+,Na+)],Ca2+与Na+的选择性比率[S(Ca2+,Na+)],Pn,Gs,xi和Rt间呈显著正相关(P＜0.01).上述结果表明,200mmol·L-1 NaCl胁迫10和30d、300mmol·L-1 NaCl胁迫10d,油菜幼苗光合抑制主要来自气孔限制,而300mmol·L-1 NaCl胁迫30d,气孔限制和非气孔限制在油菜幼苗光合抑制中均具有重要作用.Na+、Cl-、K+、Ca2+含量,Ew,u,Ls,根冠比,K+/Na+、Ca2+/Na+比值,S(K+,Na+),S(Ca2+,Na+),Pn,Gs,xi和Rt均可作为油菜生长盐适应性的评价指标.     

植物地上部分对大气CO2浓度升高的响应

大气CO2浓度升高对植物的影响，主要是促进了植物生长早期的光合作用，同时也增加了对其他资源的需求；植物的光合作用也存在对高CO2浓度的适应，不会一直维持较高的光合水平，而且植物的呼吸作用也可能会增加；大气CO2浓度升高和其他环境条件，如水分，温度和光照等对植物生长和产量存在相互作用，可以部分弥补条件的不足，也影响作物和杂草的竞争关系；自然植物群落由于有很高的多样性和复杂性，对其研究应该在生物群落水平上进行，用外推法回到植物水平，而不是相反，而且自然物种间的竞争是激烈的，CO2浓度升高或其他因素带来的任何改善，都会明显地改变竞争平衡。     

Modeling cotton (Gossypium spp.) leaves and canopy using computer aided geometric design (CAGD)

The research presented here develops a geometrically accurate model of cotton crop canopies that can be used to explore changes in canopy microenvironment and physiological function with leaf structure. We develop an accurate representation of the leaves, including changes in three-dimensional folding and orientation with age and cultivar. Photogrammetrical analysis of leaf surfaces is used to generate measured points at known positions. Interpolation of points located on the surface of the cotton leaves is then performed with a tensor product interpolants model that generates a generic leaf shape. Dynamic changes in leaf shape and canopy position over the growing season are based on measurements of cotton canopies in the field, and are used to modulate the generic leaf shape. The simulated leaves populate a canopy element based on statistical distributions from measured crop canopies. The simulation is found to give a good representation of cotton canopy leaves, adequately capturing the three-dimensional structure of the leaves and changes in leaf shape and size over the growing season. The simulated canopy accurately estimates leaf area index, except for the earliest measurement period prior to canopy closure. The application of the CAGD algorithm for representing cotton leaf and canopy geometry, and the technique for changing the leaves’ spatial position, size and shape through time of four representative cotton canopies is found to be a useful tool for developing a realistic crop canopy. We use leaf area index (LAI) as a measure of the accuracy of model-predicted LAI values in comparison to LAI in crop canopies in situ, obtaining r² values ranging from 0.82 to 0.92. The level of detail captured in the model could contribute greatly to future studies of physiological function and biophysical dynamics within a crop canopy.     

干旱胁迫对香蒲生长和叶绿素荧光参数的影响

采用野外调查方法,研究了不同土壤含水量条件下香蒲植株的形态、生物量、叶绿素含量和叶绿素荧光参数的变化。结果表明：（1）土壤含水量对香蒲株高影响显著,轻度、中度和重度干旱处理香蒲株高分别下降为对照（土壤水分始终饱和）的90.90%、68.19%和63.64%。（2）香蒲茎直径、叶长、叶宽和叶绿素含量均随土壤含水量的降低而呈递减趋势,枯叶率却明显增加。（3）不同土壤含水量条件下香蒲密度和生物量差异均达显著水平（P〈0.05）。轻度、中度和重度干旱组香蒲密度分别比对照下降41.67%、53.33%和66.67%;而对照香蒲单株生物量分别为轻度、中度和重度干旱组的2.25、5.54和7.45倍。（4）香蒲叶片最大光量子产量（Fv/Fm）和最大相对电子传递速率（Re,t,max）随土壤含水量的减少而明显降低。干旱降低了香蒲叶片光系统Ⅱ（PSⅡ）的光化学效率,抑制了香蒲的生长。     

Interactive effects of plant species diversity and elevated CO2 on soil biota and nutrient cycling

Terrestrial ecosystems consist of mutually dependent producer and decomposer subsystems, but not much is known on how their interactions are modified by plant diversity and elevated atmospheric CO2 concentrations. Factorially manipulating grassland plant species diversity and atmospheric CO2 concentrations for five years, we tested whether high diversity or elevated CO2 sustain larger or more active soil communities, affect soil aggregation, water dynamics, or nutrient cycling, and whether plant diversity and elevated CO2 interact. Nitrogen (N) and phosphorus (P) pools, symbiotic N2 fixation, plant litter quality, soil moisture, soil physical structure, soil nematode, collembola and acari communities, soil microbial biomass and microflora community structure (phospholipid fatty acid [PLFA] profiles), soil enzyme activities, and rates of C fluxes to soils were measured. No increases in soil C fluxes or the biomass, number, or activity of soil organisms were detected at high plant diversity; soil H2O and aggregation remained unaltered. Elevated CO2 affected the ecosystem primarily by improving plant and soil water status by reducing leaf conductance, whereas changes in C cycling appeared to be of subordinate importance. Slowed-down soil drying cycles resulted in lower soil aggregation under elevated CO2. Collembola benefited from extra soil moisture under elevated CO2, whereas other faunal groups did not respond. Diversity effects and interactions with elevated CO2 may have been absent because soil responses were mainly driven by community-level processes such as rates of organic C input and water use; these drivers were not changed by plant diversity manipulations, possibly because our species diversity gradient did not extend below five species and because functional type composition remained unaltered. Our findings demonstrate that global change can affect soil aggregation, and we advocate that soil aggregation should be considered as a dynamic property that may respond to environmental changes and feed back on other ecosystem functions.