澎溪河消落带典型植物群落根际土壤无机氮形态及氮转化酶活性

三峡库区消落带是典型的生态脆弱带,其土壤N循环因受到植物根际效应和季节性淹水的影响而具有特殊性.本研究以三峡库区一级支流澎溪河消落带为例,选择4种植被(狗牙根、香附子、苍耳以及玉米)覆盖区,采集植物根际、非根际土壤,分析根际土壤与非根际土壤理化性质、无机氮形态以及7种N素转化相关酶,并比较了4种植物根际效应强度,以反映不同植物覆盖对消落带土壤N循环过程的影响.研究表明:供试植物根际土壤p H值均低于非根际,有机质、全氮、全磷含量均高于非根际,表明植物根际对消落带土壤养分有富集作用;4种植物根际土壤硝态氮、铵态氮、亚硝态氮及14d可矿化氮含量均高于非根际,且土壤硝态氮、亚硝态氮以及14d可矿化氮含量呈现香附子狗牙根苍耳/玉米;总体上根际土壤N转化酶活性高于非根际,且狗牙根和香附子覆盖区脲酶、亚硝酸还原酶、谷氨酰胺酶、脱氢酶显著高于玉米和苍耳覆盖区;蛋白酶、脲酶、谷氨酰胺酶活性与4种N形态均呈显著相关性,是消落带土壤N转化的主要参与酶类;根际效应分析结果香附子和狗牙根对消落带土壤N转化的根际效应强度大于苍耳和玉米,有利于土壤N素的固定和保持.植物根际效应对消落带土壤N素循环的影响可为消落带植被恢复工程中植被选择提供参考,也为改善消落带土壤退化相关研究提供科学支撑.

Inorganic nitrogen forms and related enzyme activity of rhizosphere soils under typical plants in the littoral zone of Pengxi River

The Three Gorges Reservoir (TGR), which is the largest water conservancy project ever built in the world, produced a drawdown area of about 348.93km2 due to flooding control. The biological geochemical cycle of the soil in the drawdown zone has been changed as the result of long-term winter flooding and summer drought and vegetation covering. The loss of soil nitrogen in the drawdown zone poses a threat to the water environmental in TGR. Pengxi River, which has the largest drawdown area among all of the tributaries in TGR basin has been selected in present study. The four typical vegetation types, Cynodon dactylon, Cyperus rotundus, Anthium sibiricum and Zea mays L as control, were studied to measure nutrient characteristics and nitrogen forms of rhizosphere and non-rhizosphere soils. The variables included soil physical-chemical proprieties, ammonium nitrogen (NH4+-N), nitrate nitrogen (NO3--N), nitrite nitrogen (NO2--N), nitrogen mineralization in 14d (NN) and 7 types N invertase enzymes including protease (PR), urease (UR), nitrate reductase (NR), nitrite reductase (SNR), dehydrogenase (DE), glutaminase (GL) and asparaginase (AS). The results showed: 1) pH of rhizosphere soil was generally lower than non-rhizosphere soil under different vegetation in different type soils because of the possible organic acid and H+ released from plant roots and cation absorption differences. All nutrient concentrations in rhizosphere soil were higher than those in non-rhizosphere except potassium (Total K and available K). 2) NH4+-N, NO3--N, NO2--N and NN of rhizosphere soil were generally higher than non-rhizosphere soil, by following the order of Cyperus rotundus＞Cynodon dactylon＞Anthium sibiricum and Zea mays L under different vegetation. 3) All 7 types invertases showed the better activeness in the rhizosphere soil compared with them under non-rhizosphere. UR, SNR, DE and GL in the zone covered by Cyperus rotundus and Cynodon dactylon were significantly higher than those in Anthium sibiricum and Zea maysL. 4) There was significant correlation between soil N forms and PR, UR and GL. NO3--N was significantly correlated with SNR. Rhizosphere effects on all N forms and invertase enzyme activity were done to evaluate the incidence of the soil N cycle by different vegetations, and results showed that rhizosphere effects of Cyperus rotundus and Cynodon dactylon were greater than those of Anthium sibiricum and Zea mays L. The present research could provide that the drawdown zone covered with different vegetations has different soil processes and function for N cycle, so the vegetation recovery in the drawdown zone should consider the rhizosphere effect of different vegetations on N cycle.