Loik Michael E, Griffith Alden B, Alpert Holly, Concilio Amy L, Wade Catherine E, Martinson Sharon J
Department of Environmental Studies, University of California, 1156 High Street, Santa Cruz, CA, 95064, USA,
Oecologia. 2015 Jun;178(2):403-14. doi: 10.1007/s00442-015-3224-7. Epub 2015 Jan 28.
Snowfall provides the majority of soil water in certain ecosystems of North America. We tested the hypothesis that snow depth variation affects soil water content, which in turn drives water potential (Ψ) and photosynthesis, over 10 years for two widespread shrubs of the western USA. Stem Ψ (Ψ stem) and photosynthetic gas exchange [stomatal conductance to water vapor (g s), and CO2 assimilation (A)] were measured in mid-June each year from 2004 to 2013 for Artemisia tridentata var. vaseyana (Asteraceae) and Purshia tridentata (Rosaceae). Snow fences were used to create increased or decreased snow depth plots. Snow depth on +snow plots was about twice that of ambient plots in most years, and 20 % lower on -snow plots, consistent with several down-scaled climate model projections. Maximal soil water content at 40- and 100-cm depths was correlated with February snow depth. For both species, multivariate ANOVA (MANOVA) showed that Ψ stem, g s, and A were significantly affected by intra-annual variation in snow depth. Within years, MANOVA showed that only A was significantly affected by spatial snow depth treatments for A. tridentata, and Ψ stem was significantly affected by snow depth for P. tridentata. Results show that stem water relations and photosynthetic gas exchange for these two cold desert shrub species in mid-June were more affected by inter-annual variation in snow depth by comparison to within-year spatial variation in snow depth. The results highlight the potential importance of changes in inter-annual variation in snowfall for future shrub photosynthesis in the western Great Basin Desert.
降雪为北美某些生态系统提供了大部分土壤水分。我们对一个假设进行了为期10年的测试，该假设认为降雪深度变化会影响土壤含水量，进而驱动水势（Ψ）和光合作用，研究对象为美国西部两种分布广泛的灌木。在2004年至2013年期间，每年6月中旬测量了三齿蒿（菊科）和三齿苦艾（蔷薇科）的茎水势（Ψ茎）以及光合气体交换[气孔导度（gs）和二氧化碳同化量（A）]。使用雪栅栏来创建增加或减少降雪深度的样地。在大多数年份，+雪样地的降雪深度约为对照样地的两倍，而 - 雪样地的降雪深度低20%，这与几个降尺度气候模型预测结果一致。40厘米和100厘米深度处的最大土壤含水量与2月的降雪深度相关。对于这两个物种，多变量方差分析（MANOVA）表明，Ψ茎、gs和A受降雪深度年内变化的显著影响。在各年份内，MANOVA表明，对于三齿蒿，只有A受空间降雪深度处理的显著影响，而对于三齿苦艾，Ψ茎受降雪深度的显著影响。结果表明，与降雪深度的年内空间变化相比，这两种寒冷沙漠灌木物种在6月中旬的茎水关系和光合气体交换受降雪深度年际变化的影响更大。这些结果突出了降雪年际变化的改变对大盆地沙漠西部未来灌木光合作用的潜在重要性。
