Calibration of a multi-species model for chlorophyll estimation in seedlings of Neotropical tree species using hand-held leaf absorbance meters and spectral reflectance

The aim of the present study was to calibrate a multi-species model for assessing leaf chlorophyll content in seedlings of six Neotropical rainforest tree species. Two hand-held chlorophyll absorbance meters (SPAD-502 and ClorofiLog) and the chlorophyll normalized difference leaf reflectance index (ND705) were tested. Measurements of leaf absorbance and reflectance, contents of chlorophyll a (Chl a), chlorophyll b (Chl b), and total chlorophyll (Chl t), leaf area (LA), and leaf mass per area (LMA) were performed on fully expanded leaves. A total of 200 leaves were used for the calibration of the multiple-species model. The relative root mean square calibration errors (RMSεc, %) were calculated based on estimated chlorophyll values for multiple-species models and on measured values for each of the six species. The average values of LA varied between 14.2 and 29.5 cm-2, LMA between 34.8 and 98.9 g m-2, and Chl t between 3 and 815 mg m-2. For all indices, the highest values of the coefficients of determination (R2) were observed for Chl a (R2 ≥ 0.91), followed by Chl t (R2 ≥ 0.89) and Chl b (R2 ≥ 0.82). The highest values of R2 were obtained for ND705 (R2 ≥ 0.86) followed by SPAD-502 (R2 ≥ 0.83) and ClorofiLog (R2 ≥ 0.82). The present study showed that ClorofiLog and SPAD-502 indices could be safely interconverted by a simple linear regression model (R2 = 0.98). RMSεc values were lower than 20%, which confirmed the feasibility of the multi-species model for estimating the chlorophyll content using hand-held chlorophyll absorbance meters and leaf reflectance

Osmotic adjustment, proline accumulation and cell membrane stability in leaves of Cocos nucifera submitted to drought stress

The role of drought-induced proline accumulation in coconut leaves is still unclear. With the objective of evaluating the impact of water shortage on leaf osmotic potential, proline accumulation and cell membrane stability in young plants of two Brazilian Green Dwarf coconut ecotypes from contrasting areas (Brazilian Green Dwarf from Una, Bahia, UGD, and from Jiqui, Rio Grande do Norte, JGD), a pot experiment was conducted under greenhouse conditions. Three drought cycles consisting of suspension of irrigation until the net photosynthetic rate (A) approached zero and rewatering until recovery of A to 85% of the irrigated control plants. Pre-dawn leaf water potential (ΨPD) reached −1.2 MPa at the point of maximum stress (PMS). Dry matter production and leaf area were severely reduced by drought treatment in the two ecotypes. Corrected values of osmotic potential were significantly reduced in stressed plants of the two ecotypes. Green dwarf coconut palm showed low osmotic adjustment (from 0.05 to 0.24 MPa) and significant accumulation of proline (from 1.5 to 2.1 times in relation to control) in leaflets in response to water deficit. Considering the growth reduction observed in both ecotypes, proline was not associated to osmoregulation. On the other hand, the absence of membrane damage, as indicated by electrolyte leakage method, suggests that the protective role of proline in this specie can be more important. The two ecotypes of Green dwarf coconut palm behaved similarly in the present experiment for most traits evaluated. Slight differences among the ecotypes were observed with respect to the response to treatments, such as higher proline accumulation in JGD

Photosynthetic limitations in leaves of young Brazilian Green Dwarf coconut (Cocos nucifera L. ‘nana’) palm under well-watered conditions or recovering from drought stress

Young plants of two Brazilian Green Dwarf coconut ecotypes from contrasting regions in relation to climate (UGD, from a hot and humid climate and JGD, from a hot and dry climate) were submitted to three consecutive drying/recovery cycles, under greenhouse conditions to determine the photosynthetic limitations encountered during the recovery phase of water deficiency. Three hypotheses were tested: (1) non-stomatal factors contribute to the incomplete recovery of net photosynthesis rate (A), (2) photochemical impairment is an important component of the non-stomatal limitations to A and (3) the two coconut ecotypes respond differently to the drought recovery. In each drying/recovery cycle, irrigation was suppressed until A reached zero. Then the plants were rewatered and the recovery was accompanied for 8 days. After 4 days of rewatering, CO2 and light response curve parameters were used to discriminate the stomatal and non-stomatal factors contributing to the incomplete recovery of A. Upon rewatering for 4 days, the pre-dawn leaf water potential of the stressed plants increased from −1.20 to −0.15 MPa on average. Only small differences were detected in the intercellular to atmospheric CO2 concentration ratio but A did not recover completely to the control values. In both ecotypes, light and CO2-saturated A, carboxylation efficiency, maximum quantum yield of PSII and maximum electron transport rate were significantly lower in stressed plants in comparison with the well-watered ones. Relative stomatal limitation (LS) ranged from 16 to 20% without significant differences between treatments and between ecotypes. The relative mesophyll limitation (Lm) was significantly higher in JGD in cycle 1 but this changed after repeated drought stress, decreasing to values significantly lower than those in UGD in the other two cycles. The results showed that after 4 days of rewatering stressed plant stomatal limitations were comparable to that of well-watered control plants (∼20%). However A did not recover completely after drought stress due to non-stomatal factors. Important differences between the ecotypes were identified. The ecotype JGD presented smaller Lm, faster recovery of the apparent quantum efficiency of CO2 assimilation, adjustment of some carbon balance components and signs of photosynthetic capacity acclimation after repeated drying/recovery cycles

Stomatal control of transpiration in the canopy of a clonal Eucalyptus grandis plantation

Predawn leaf water potential, stomatal conductance and microclimatic variables were measured on 13 sampling days from November 1995 through August 1996 to determine how environmental and physiological factors affect water use at the canopy scale in a plantation of mature clonal Eucalyptus grandis Hill ex-Maiden hybrids in the State of Espirito Santo, Brazil. The simple ”big leaf” Penman-Monteith model was used to estimate canopy transpiration. During the study period the predawn leaf water potential varied from –0.4 to –1.3 MPa, with the minimum values observed in the winter months (June and August 1996), while the average estimated values for canopy conductance and canopy transpiration fell from 17.3 to 5.8 mm s–1 and from 0.54 to 0.18 mm h–1, respectively. On the basis of all measurements, the average value of the decoupling coefficient was 0.25. During continuous soil water shortage a proportional reduction was observed in predawn leaf water potential and in daily maximum values of stomatal conductance, canopy transpiration and decoupling coefficient. The results showed that water vapour exchange in this canopy is strongly dominated by the regional vapour pressure deficit and that canopy transpiration is controlled mainly by stomatal conductance. On a seasonal basis, stomatal conductance and canopy transpiration were mainly related to predawn leaf water potential and, thus, to soil moisture and rainfall. Good results were obtained with a multiplicative empirical model that uses values of photosynthetically active radiation, vapour pressure deficit and predawn leaf water potential to estimate stomatal conductance

Some photosynthetic and growth responses of Annona glabra L. seedlings to soil flooding Algumas respostas fotossintéticas e do crescimento de plântulas de Annona glabra L. ao alagamento do solo

An experiment was conducted with the aim to analyze the effects of soil flooding and leaf position on net primary productivity and whole plant carbon balance of Annona glabra L. (Annonaceae) seedlings, a highly flood-tolerant tree, native to the tropical Americas. All seedlings survived a period of 56 days of flooding without symptoms of stress. Flooding induced significant increments in root, stem and whole-plant biomass (P <0.01), and in the root:shoot mass ratio (P <0.05). Measurements of leaf gas exchange were conducted at days four, 11, 18 and 56 after flooding, on the first (L1), fourth (L4) and seventh (L7) fully expanded leaves from the apex of each seedling. The mean values of stomatal conductance to water vapour (g s) and net photosynthetic rate (A) in the control seedlings were around 0.26 mol m-2s-1 and 8.8 µmol m-2s-1, respectively. Significant reductions (P <0.05) in A were observed from L1 to L7 in controls at all four days of measurements. Reductions in A with increasing leaf age also ocurred for flooded plants, but only at days four and 18. Flooding induced significant changes in gs (P <0.05), reaching 65% of controls at day four but 152% of controls at day 56. Based on the results we conclude that the high survival and growth rates of A. glabra seedlings are directly related to the capacity to mantain a high stomatal conductance and net photosynthetic rate under soil flooding.<br>Um experimento foi conduzido com o objetivo de analisar os efeitos do alagamento e da posição das folhas na produtividade primária líquida e no balanço de carbono em plântulas de Annona glabra L. (Annonaceae), uma espécie altamente tolerante ao alagamento e nativa na América tropical. Todas as plântulas sobreviveram ao período de alagamento de 56 dias sem apresentarem sintomas de estresse. O alagamento induziu incrementos significativos (P <0,01) na biomassa de raízes, caules e planta inteira, e na razão raízes/parte aérea. Medições das trocas gasosas foliares foram conduzidas aos quatro, 11, 18 e 56 dias após o alagamento, na primeira (L1), quarta (L4) e sétima (L7) folha completamente expandida a partir do ápice em cada plântula. Os valores médios da condutância estomática ao vapor de água (g s) e da taxa fotossintética líquida (A) nas plântulas controle foram 0,26 mol m-2s-1 e 8,8 µmol m-2s-1, respectivamente. Reduções significativas (P <0,05) em A foram observadas entre L1 e L7 nas plântulas controle em todos os três dias de medições. As reduções em A com o aumento da idade foliar também ocorreram nas plantas alagadas, apenas nos dias 4 e 18. O alagamento induziu alterações significativas em gs (P <0,05), alcançando 65% em relação ao controle no dia 4 e 152% em relação ao controle no dia 56. Com base nos resultados obtidos foi possível concluir que as elevadas taxas de sobrevivência e de crescimento de plântulas de A. glabra estão diretamente relacionadas com a capacidade de manter elevados valores de condutância estomática e de taxa fotossintética líquida em condições de alagamento do solo

Key leaf traits indicative of photosynthetic plasticity in tropical tree species

Information about light tolerance and photosynthetic plasticity of indigenous tropical tree species is still limited, particularly information of first years of plants’ development. In this study, we evaluated the adjustments in response to different light environments of 25 leaf traits most commonly assessed in studies on light acclimation of photosynthesis in current literature. This evaluation was used to investigate the photosynthetic plasticity on young plants of five tropical tree species belonged to different successional groups. All the species are commonly used in forest restoration programs in Brazil. Plants were grown for 6 months under different light conditions simulating environments that could exist due to variation in naturally occurring canopy openings of secondary tropical forests. The level of adjustment on leaf traits to environmental conditions was calculated via a plasticity index. The relation between leaf trait adjustments and species photosynthetic plasticity was investigated by multivariate Biplot analyses. We selected the seven most explicative leaf traits of the photosynthetic plasticity of the studied species in response to different light environments: dark respiration rate (R d), Rubisco carboxylation capacity (V cmax), total chlorophyll content (ChlT), contribution of spongy parenchyma (%SP), contribution of leaf collenchyma tissue (%C), chlorophyll parenchyma thickness (PP/SP) and specific leaf area (SLA). Based on the selected traits, we identified the traits most related to high plasticity (V cmax, PP/SP, %SP, %C and SLA) and low plasticity (V cmax, R d and ChlT) and grouped species into three different patterns of photosynthetic plasticity. Our plasticity grouping was not correlated with species successional classification, indicating the importance of including physiological features related to light tolerance in species successional classifications. This work provides complementing information to traditional species successional groupings and to our current ability to select species for enrichment planting on restoration efforts