## 1 Introduction  
Precipitation is one of the dominant climatic drivers regulating abiotic and biotic ecosystem processes and functions, such as drought-induced wildfire and plant mortality, wet-promoted soil mineralization, and terrestrial carbon sink. Drought stress likely increases under a warming climate, which has potential implications for biodiversity and ecosystem services [1; 2]. For example, drought tends to shift community composition from mesic species-dominated toward xeric species-dominated [1; 3] and may change the global terrestrial net primary production (NPP) [4]. On the contrary, wet conditions enhance the water availability of terrestrial ecosystems and thus increase gross primary productivity (GPP) and enhance land carbon sink [5; 6]. Warming is expected to intensify the hydrological cycle, but it was spatially heterogeneous across the globe [7; 8]. A concise pattern, \"dry gets drier and wet gets wetter\", has been especially proposed and evidenced in some studies, which is robust over the oceanic tropics but indistinct over lands [9; 10; 11]. [PERSON] et al. (2014) examined the pattern and found it was demonstrated over only 10.8% of the global lands, while 9.5% of the lands showed the opposite pattern [8]. Temporally, an intensified hydrological cycle is manifested in not only reshaping the precipitation amount but also the variability, including seasonality, frequency, and extremes. It was proved that over two-thirds of the Northern Hemisphere land area has experienced intensified heavy precipitation events [12]. The increase in extreme daily precipitation over both dry and wet regions on the earth is also historically observed and projected by climate models [7]. For example, the seasonality and frequency of precipitation have been evidenced in China, where winter precipitation over the northwest and southwest increased dramatically between the 1960s and the 2010s [13] and precipitation frequency increased notably in south China [14]. However, the spatial and temporal change patterns of precipitation and their potential impacts on terrestrial ecosystems under climate warming have not been comprehensively evaluated. Effects of altered precipitation regimes on plants depend on both the abiotic (e.g., precipitation and soil texture) and biotic factors (e.g., plant species and traits) [15; 16; 17]. Heavy precipitation events are effective in infiltration and increase deep soil moisture, which improves water availability and benefits the photosynthetic production of plants with deep roots [18; 19; 20]. Small precipitation events tend to increase surface soil moisture and might be stimulations for microbial respiration and plants with shallow roots [16; 19]. However, more precipitation in the early or late growing season may mismatch the large water demand and water supply in the middle growing season thus reducing plant productivity [21]. On the other hand, the biotic acclimation or adaptation of plants (or communities) also mitigates the impacts of water supply through biomass allocation and shifting dominated species. For example, a recent meta-analysis examining the response of plant biomass allocation to drought showed that drought significantly increases the root mass meanwhile decreasing stem, leaf, and reproductive mass [22]. With a 4-year experimental drought treatment on alpine grassland, previous study also suggested that drought does not affect total NPP but shifts more NPP allocation belowground [3]. Therefore, the response of plants (or communities) to precipitation change may be diverse in structure and function [23]. The Tibetan Plateau (TP), known as the \"Third Pole\" of the world, is the highest plateau on the earth [24]. Vegetation productivity (biomass) and respirations on the TP were extremely sensitive to climate change [25; 26; 27; 28]. Generally, low temperature is widely recognized as the limited climatic factor for vegetation growth and carbon budgets overall the TP [29; 30; 31; 32]. The dominant driver is spatially heterogeneous [26; 33].