The rapid green fodder expansion in native grassland and cropland in the northeastern Tibetan Plateau (a rain-fed region), driven by the increasing forage demand, has altered vegetation patterns and potentially affected carbon and water cycles. To clarify the elusive effects of green fodder expansion on the carbon sequestration and water consumption in this region, we examined its impacts on productivity, evapotranspiration, and water-use efficiency using a pairwise comparison approach at seasonal and annual scales in 2019. We also conducted an attribution analysis to undercover the mechanisms through which green fodder expansion influences water-use efficiency. Our results revealed that during the growing season, gross primary productivity in green fodder lands was 12.25 % and 4.14 % higher than the adjacent grasslands and croplands, respectively. Evapotranspiration was 2.89 % and 3.33 % lower in comparison. Ecosystem-level water-use efficiency was respectively 15.14 % and 6.92 % higher, while plant-level water-use efficiency increased by 4.76 % and 1.5 %, respectively. Green fodder expansion enhanced ecosystem-level water-use efficiency by increasing gross primary productivity and reducing evapotranspiration, while improvements in plant-level water-use efficiency were mainly driven by gross primary productivity increases. The changes in plant physiology and canopy structure induced by green fodder cultivation enhanced the CO2 assimilation capacity, reduced soil evaporation, and allocated more water toward transpiration, emerging as the dominant factors driving the observed changes in gross primary productivity and evapotranspiration. However, we found that green fodder planting also led to increased soil evaporation over the non-growing season, which partially offset its positive effect on water-use efficiency during the growing season. This study suggests that green fodder cultivation could be a potential solution to increasing forage supply in the northeastern Tibetan Plateau, while highlighting the necessity of reducing soil evaporation during the non-growing season to maximize the benefits of green fodder expansion.

中文翻译：

---

青贮饲料向草原和农田扩张诱导的生理变化提高了青藏高原东北部的水分利用效率


在青藏高原东北部（雨养地区）原生草地和农田中，由于饲料需求增加，绿色饲料迅速扩张，改变了植被模式，并可能影响碳和水循环。为了阐明绿色饲料扩张对该地区碳封存和水消耗的难以捉摸的影响，我们在 2019 年使用季节性和年度尺度的成对比较方法研究了其对生产力、蒸散和水分利用效率的影响。我们还进行了归因分析，以揭示绿色饲料扩张影响水利用效率的机制。结果表明，在生长季，青草地的初级毛生产力分别比相邻草地和农田高 12.25 % 和 4.14 %。相比之下，蒸散量分别低 2.89% 和 3.33%。生态系统层面的水分利用效率分别提高了 15.14 % 和 6.92%，而植物层面的水分利用效率分别提高了 4.76% 和 1.5%。绿色饲料的扩张通过提高总初级生产力和减少蒸散来提高生态系统水平的水分利用效率，而植物水平水分利用效率的提高主要是由总初级生产力的提高驱动的。青饲料栽培诱导的植物生理和冠层结构变化增强了 CO2 同化能力，减少了土壤蒸发，并为蒸腾分配了更多的水分，成为驱动观察到的总初级生产力和蒸散变化的主导因素。 然而，我们发现，绿色饲料种植也导致非生长季节土壤蒸发增加，这部分抵消了其对生长季节水分利用效率的积极影响。这项研究表明，绿色饲料种植可能是增加青藏高原东北部饲料供应的潜在解决方案，同时强调了在非生长季节减少土壤蒸发以最大限度地发挥绿色饲料扩张效益的必要性。