Canopy Rainfall Storage Capacity Related To Canopy Properties Along Sub-alpine Meadow Degradation Gradient

Canopy rainfall storage capacity (S) is not only an important parameter in rainfall interception models, but it also affects others processes such as pollutant deposition, spread of plant disease, gas exchange processes, and photosynthesis. Most studies on S have concentrated on forests, while there is a paucity of information about S by grasslands. Sub-alpine meadow degradation is expected to change S because of reduced vegetation biomass and leaf area index (LAI) as well as changed species composition. In this study, we aimed to:(1) use the water soakage method and the water budget method to estimate S along sub-alpine meadow degradation gradient (non-degraded, lightly degraded and moderately degraded) in the Qinghai-Tibetan Plateau, China and explore the eco-hydrological significance of changes in S;(2) evaluate the effects of changes in species composition on S;(3) compare the water soakage method with the water budget balance method;(4) relate S to canopy properties and figure out how to improve the linear relationship between S and LAI.The results showed that:1. Sub-alpine meadow degradation significantly reduced S (P<0.05). In non-degraded, lightly degraded and moderately degraded sub-alpine meadows, S estimated using the water soakage method were0.612±0.08mm,0.289±0.04mm, and0.217±0.01mm; S estimated using the water budget balance method were0.979±0.32mm,0.493±0.13mm, and0.419±0.09mm. While evaluating the eco-hydrological significance of significant reduction in S along sub-alpine meadow degeneration gradient, it is particularly important to consider the evaporation (E) during rainfall.2. The effects of changes in species composition on S was highlighted by the fact that the reduction in S was firstly more than and then less than the proportional reduction in LAI along sub-alpine meadow degradation gradient. This could be explained by the following:(1) Specific storage capacity per unit one-sided leaf area (SLM) of Potentilla arserina (0.268mm) was approximately2.5times greater than that of graminoid plants (0.106mm).(2) In non-degraded sub-alpine meadow, Potentilla arserina was the dominant species and accounted for31.18%of the total leaf area; in lightly degraded sub-alpine meadow, graminoid plants were the dominant species and accounted for44.41%of the total leaf area, while Potentilla arserina was a rare species with a leaf area of only3.76%; in moderately degraded sub-alpine meadow, Potentilla arserina was the dominant species with a leaf area of19.91%. We conclude that the difference of SLM among different species and the magnitude of change in each species leaf area relative to the total leaf area along sub-alpine meadow degeneration gradient together determine the effects of changes in species composition on S. Larger interspecific differences in SLM and in the magnitude in species leaf area relative to the total leaf area are associated with larger effects of species composition on S.3. S estimated using the water soakage method was significantly lower than S estimated using the water budget balance method (P<0.05).4. Compared with canopy coverage, LAI was a stronger predictor of the variability in S. The stem rainfall storage capacity by sub-alpine meadow was extremely low and consequently it could not greatly degrade the linear relationship between S and LAI. This was also why the linear relationship between S and LAI was not be singnificantly improved after converting fresh weight of stem tissues into effective leaf area of the corresponding species for intercepting rainfall. Introducing a coefficient of leaf area (c) according to differences in SLM among different species significantly improved the linear relationship between S and LAI.