Warming and spring precipitation addition change plant growth pattern but have minor effects on growing season mean gross ecosystem productivity in an alpine meadow.

Gross ecosystem productivity (GEP) plays an important role in global carbon cycling. However, how plant phenology and growth rate regulate GEP under climate change is unclear. Based on an in situ manipulative experiment using open top chambers from 2015 to 2018, we measured whole year warming and spring precipitation addition effects on plant phenology, plant growth rate and GEP. Our results showed that warming delayed plant green up (4 days) and withering (5 days), while spring precipitation addition advanced green up 13 days and did not change withering. Warming delayed the timing of the fast-growing phase 7 days, shortened length of the fast-growing phase 7 days and marginally increased the growth rate. Spring precipitation addition advanced the timing of the fast-growing phase 6 days, but did not change the length of the fast-growing phase or the growth rate. Both whole year warming and spring precipitation addition have not significantly affected growing season mean GEP. GEP is positively correlated with plant growth rate and negatively correlated with the length of the fast-growing phase. We provide an evidence that although warming did not change growing season mean productivity, it delayed plant fast-growing phase. Our findings suggest that management approaches for increasing water availability before the fast-growing phase should be intensified to increase ecosystem carbon uptake and grass supply for animal husbandry in spring.