作物生产、水分消耗与水分利用效率间的动态联系

在对水分消耗与产量（或同化物生产）关系剖析的基础上，引入边际水分利用效率与水分生产弹性系数概念，探讨具有动态特征的作物生产、水分消耗与水分利用效率间的内在联系。就作物产量层次上的水分利用效率而论，当Ｙ＝ｆ（ＥＴ）表现为线性时，ＷＵＥ随ＥＴ的变化趋势直接受常数项的取值条件的影响；当Ｙ＝ｆ（ＥＴ）表现为二次抛物线时，随着ＥＴ的增加，ＷＵＥ的最大值要先于Ｙ的最大值而提前达到，使ＷＵＥ达到最大值的ＥＴ值等于常数项与二次项系数之比的算术平方根，在其之前，ＷＵＥ渐增，在其之后，ＷＵＥ渐降。     

Interactive effects of multiscale diversification practices on farmland bird stress

Farmland diversification practices (i.e., methods used to produce food sustainably by enhancing biodiversity in cropping systems) are sometimes considered beneficial to both agriculture and biodiversity, but most studies of these practices rely on species richness, diversity, or abundance as a proxy for habitat quality. Biodiversity assessments may miss early clues that populations are imperiled when species presence does not imply persistence. Physiological stress indicators may help identify low-quality habitats before population declines occur. We explored how avian stress indicators respond to on-farm management practices and surrounding seminatural area (1-km radius) across 21 California strawberry farms. We examined whether commonly used biodiversity metrics correlate with stress responses in wild birds. We used ∼1000 blood and feather samples and body mass and wing chord measurements, mostly from passerines, to test the effects of diversification practices on four physiological stress indicators: heterophil to lymphocyte ratios (H:L), body condition, hematocrit values, and feather growth rates of individual birds. We then tested the relationship between physiological stress indicators and species richness, abundance, occurrence, and diversity derived from 285 bird point count surveys. After accounting for other biological drivers, landscape context mediated the effect of local farm management on H:L and body condition. Local diversification practices were associated with reduced individual stress in intensive agricultural landscapes but increased it in landscapes surrounded by relatively more seminatural area. Feathers grew more slowly in landscapes dominated by strawberry production, suggesting that nutritional condition was lower here than in landscapes with more crop types and seminatural areas. We found scant evidence that species richness, abundance, occurrence, or diversity metrics were correlated with the individual's physiological stress, suggesting that reliance on these metrics may obscure the impacts of management on species persistence. Our findings underscore the importance of considering landscape context when designing local management strategies to promote wildlife conservation.