Non-structural carbohydrate levels of three co-occurring understory plants and their responses to forest thinning by gap creation in a dense pine plantation

We investigated non-structural carbohydrates (NSC) levels and components (starch, glucose, fructose and sucrose) in the leaves of three typical co-occurring forest-floor plants, moss Eurhynchium savatieri (ES), fern Parathelypteris nipponica (PN) and forb Aruncus sylvester (AS) in a 30-year-old Chinese pine (Pinus tabulaeformis) plantation forest on the eastern Tibetan Plateau. We also explored their responses to three gap creation treatments (control and two gap creations of 80 and 110 m(2)) based on NSC levels. PN had the highest leaf NSC level of the three plants, with AS second and ES lowest. Starch was the predominant component of NSC and the contents of glucose were higher than those of fructose or sucrose for all three species. The NSC level of ES in intermediate gaps was significantly higher than at control sites. PN also had higher NSC levels in both small and intermediate gaps than in control sites. But the differences between treatments were not obvious for AS. Our results suggest that ES and PN benefit from gap formation while the two species have different NSC response sensitivities to gap size, but the leaf NSC level of AS is less sensitive to the disturbance.