Effect of fruit load and girdling on leaf photosynthesis in Mangifera indica L
2004
Utina, N. I (Natalʹi︠a︡ Ieronimovna) | Lechaudel, M. | Lu, Ponzy
Leaf nitrogen concentration (N(m)), mass-to-area ratio, amount of nitrogen per unit leaf area (N(a)), non-structural carbohydrate concentration (TNC(a)), maximal rate of carboxylation (V(cmax)), light-saturated rate of photosynthetic electron transport (J(max)), dark respiration (R(d)), net photosynthetic assimilation (A(net)), quantum yield of photosystem II (phi(PSII)), and intercellular CO2 concentration (C(i)) were measured in Mangifera indica L. leaves on three types of fruit-bearing branches (non-girdled, NG; girdled with high (HFL) and low (LFL) fruit load), experiencing similar light exposure. TNC(a), V(cmax)/N(a), J(max)/N(a), R(d)/N(a), C(i), and the initial quantum yield of photosynthetic electron transport (alpha) were similar in both HFL and NG treatments, but N(m), N(a), and photosynthetic capacity parameters (V(cmax) and J(max)) were lower in the HFL than in the NG treatment. The strong depressing effect of girdling on leaf nitrogen concentration cannot therefore be attributed to a change in TNC(a). By contrast, N(a) and TNC(a) were lower and higher, respectively, in the LFL than in the HFL treatment, suggesting that carbohydrate content may become the driving force behind photosynthetic acclimation to changing source-sink relationships, like the ones resulting from the presence of developing fruits. V(cmax)/N(a) and J(max)/N(a) were lower in the LFL than in the HFL treatment, while R(d)/N(a), C(i), and alpha were not affected by fruit load. It is concluded that girdling and high fruit load affect photosynthesis permanently by decreasing and increasing, respectively, leaf nitrogen concentration. Fruit load, moreover, may have an additional effect on photosynthetic capacity by affecting the relationship between V(cmax) and J(max), and N(a).
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