02885naa a2200277 a 450000100080000000500110000800800410001902200140006002400360007410000200011024501380013026000090026850001080027752019510038565300180233665300290235465300260238365300090240965300200241865300190243865300110245765300250246870000140249370000140250777300860252110127632019-10-08       2003    bl uuuu     u00u1 u    #d  a0829-318X7 a10.1093/treephys/23.13.8992DOI1 aSYVERTSEN, J.P.  aFruit load and canopy shading affect leaf characteristics and net gas exchange of 'Spring' navel orange trees.h[electronic resource]  c2003  aArticle history: Received December 11, 2002 / Accepted March 8, 2003 / Published online August 1, 2003.  aABSTRACT. Five-year-old 'Spring' navel (Citrus sinensis (L.) Osbeck) orange trees were completely defruited, 50% defruited or left fully laden to study effects of fruit load on concentrations of nitrogen (N) and carbohydrate, net assimilation of CO2 (Ac) and stomatal conductance (g s) of mature leaves on clear winter days just before fruit harvest. Leaves on defruited trees were larger, had higher starch concentrations and greater leaf dry mass per area (LDMa) than leaves on fruited trees. Both Ac and gs were more than 40% lower in sunlit leaves on defruited trees than in sunlit leaves on trees with fruit. Leaves immediately adjacent to fruit were smaller, had lower leaf nitrogen and carbohydrate concentrations, lower LDMa and lower Ac than leaves on non-fruiting branches of the same trees. Removing half the crop increased individual fruit mass, but reduced fruit color development. Half the trees were shaded with 50% shade cloth for 4 months before harvest to determine the effects of lower leaf temperature (T1) and leaf-to-air vapor pressure difference on leaf responses. On relatively warm days when sunlit T1 > 25°C, shade increased Ac and gs, but had no effect on the ratio of internal to ambient CO2 (C i/Ca) concentration in leaves, implying that high mesophyll temperatures in sunlit leaves were more important than gs in limiting Ac. Sunlit leaves were more photoinhibited than shaded leaves on cooler days when T1 < 25°C. Shade decreased total soluble sugar concentrations in leaves, but had no effect on leaf starch concentrations. Shading had no effects on canopy volume, yield or fruit size, but shaded fruit developed better external color than sun-exposed fruit. Overall, the presence of a normal fruit crop resulted in lower foliar carbohydrate concentrations and higher Ac compared with defruited trees, except on warm days when Ac was reduced by high leaf temperatures. Copyright © 2003, Oxford University Press  aCarbohydrates  aChlorophyll fluorescence  aLeaf CO2 assimilation  aLVPD  aPhotoinhibition  aSoluble sugars  aStarch  aStomatal conductance1 aGOÑI, C.1 aOTERO, A.  tTree Physiology, September 2003, Volume 23, Issue 13, Pages 899-906. OPEN ACCESS.