She Weiwei, Zhang Yuqing, Qin Shugao, Wu Bin, Bai Yuxuan
Yanchi Research Station, School of Soil and Water Conservation, Beijing Forestry University Beijing, China.
Yanchi Research Station, School of Soil and Water Conservation, Beijing Forestry UniversityBeijing, China; Key Laboratory of State Forestry Administration on Soil and Water Conservation, Beijing Forestry UniversityBeijing, China.
Front Plant Sci. 2016 Dec 20;7:1908. doi: 10.3389/fpls.2016.01908. eCollection 2016.
Shrublands are one of the major types of ecosystems in the desert regions of northern China, which is expected to be substantially more sensitive to global environmental changes, such as widespread nitrogen enrichment and precipitation changes, than other ecosystem types. However, the interactive effects of nitrogen and precipitation on them remain poorly understood. We conducted a fully factorial field experiment simulating three levels of precipitation (ambient, +20%, +40%) and with two levels of nitrogen deposition (ambient, 60 kg N ha yr) in a desert shrubland in the Mu Us Desert of northern China. We used plant architectural traits (plant cover, volume, twig size and number) as proxies to predict aboveground net primary productivity (ANPP) of the dominant shrub ( Krasch), and assessed the responses of plant productivity and architectural traits to water and nitrogen addition. We found significant differences in twig size and number of under water and nitrogen treatments but not in shrub cover/volume, which suggest that twig size and number of the shrub species were more sensitive to environmental changes. The productivity of the overall community was sensitive to increased precipitation and nitrogen, and shrubs played a more important role than herbaceous plants in driving productivity in this ecosystem. Precipitation- and nitrogen-induced increases in vegetation production were positively associated with increases in twig size and number of the dominant shrub. Water addition enhanced the twig length of , while nitrogen addition resulted in increased twig density (the number of twigs per square meter). Water and nitrogen interacted to affect twig length, but not twig number and shrub ANPP. The trade-off, defined as negative covariance between twig size and number, was likely the mechanism underlying the responses of twig length and shrub ANPP to water and nitrogen interactions. Our results highlight the sensitivity of twig size and number as indicators to estimate shrub production and the mechanism underpinning desert shrub ANPP response to global environmental changes.
灌丛是中国北方沙漠地区主要的生态系统类型之一，预计它对全球环境变化（如广泛的氮富集和降水变化）的敏感度要远高于其他生态系统类型。然而，氮和降水对其的交互作用仍知之甚少。我们在中国北方毛乌素沙漠的一个荒漠灌丛中进行了一项全因子田间试验，模拟了三个降水水平（ ambient、 +20%、 +40%）和两个氮沉降水平（ ambient、 60 kg N ha yr）。我们使用植物结构性状（植被覆盖度、体积、小枝大小和数量）作为指标来预测优势灌木（柠条）的地上净初级生产力（ ANPP），并评估植物生产力和结构性状对水分和氮添加的响应。我们发现，在水分和氮处理下，小枝大小和数量存在显著差异，但灌木覆盖度/体积没有差异，这表明灌木物种的小枝大小和数量对环境变化更敏感。整个群落的生产力对降水增加和氮添加敏感，并且在该生态系统中，灌木在驱动生产力方面比草本植物发挥了更重要的作用。降水和氮诱导的植被产量增加与优势灌木的小枝大小和数量增加呈正相关。水分添加增加了柠条的小枝长度，而氮添加导致小枝密度增加（每平方米小枝数量）。水分和氮相互作用影响小枝长度，但不影响小枝数量和灌木 ANPP。权衡（定义为小枝大小和数量之间的负协方差）可能是小枝长度和灌木 ANPP对水分和氮相互作用响应的潜在机制。我们的结果突出了小枝大小和数量作为估计灌木产量指标的敏感性，以及荒漠灌木 ANPP对全球环境变化响应的潜在机制。
