Abstract. Coexisting plant species in a karst ecosystem may use diverse strategies of
trade off between carbon gain and water loss to adopt to the low soil
nutrient and low water availability conditions. An understanding of the impact of
CO2 diffusion and maximum carboxylase activity of Rubisco
(Vcmax) on the light-saturated net photosynthesis (A) and
intrinsic water use efficiency (iWUE) can provide insight into physiological
strategies of the water–carbon regulation of coexisting plant species used in
adaptation to karst environments at the leaf scale. We selected 63 dominant
species (across 6 life forms) in a subtropical karst primary forest in
southwestern China, measured their CO2 response curves, and calculated
the corresponding stomatal conductance to CO2 (gs), mesophyll
conductance to CO2 (gm), and Vcmax. The results showed that
gs and gm varied about 7.6- and 34.5-fold, respectively,
and that gs was positively related to gm. The contribution of gm
to the leaf CO2 gradient was similar to that of gs. gs ∕ A,
gm ∕ A and gt ∕ A was negatively related to Vcmax ∕ A. The
relative limitations of gs (ls), gm (lm), and Vcmax
(lb) to A for the whole group (combined six life forms) were
significantly different from each other (P < 0.05). lm was the
largest (0.38 ± 0.12), followed by lb (0.34 ± 0.14), and
ls (0.28 ± 0.07). No significant difference was found between ls, lm, and lb for trees
and tree/shrubs, while lm was the largest, followed by lb and ls for shrubs, grasses, vines and ferns
(P < 0.05). iWUE varied about 3-fold (from 29.52 to 88.92 µmol CO2 mol−1 H2O) across all species, and was significantly
correlated with gs, Vcmax, gm ∕ gs, and Vcmax ∕ gs.
These results indicated that karst plants maintained relatively high A and
low iWUE through the covariation of gs, gm, and Vcmax
as an adaptation to a karst environment.
Life forms, leaf size spectra, regeneration capacity and diversity of plant species grown in the Thandiani forests, district Abbottabad, Khyber Pakhtunkhwa, Pakistan
