Biomassa, trocas gasosas e aspectos nutricionais de plantas jovens de pau de balsa (Ochroma pyramidale (Cav. Ex Lamb.) Urb.) submetidas à fertilização fosfatada em ambientes contrastantes de irradiância

The irradiance and nutrient supply affect the assimilation of carbon and influence the gain and biomass partition. The aim of this research was to investigate the growth and photosynthesis in young plants of Ochroma pyramidale subjected to contrasting light environments and phosphorus fertilization. Young plants of O. pyramidale were exposed to two irradiance levels (Low: 10 to 15 and High: 1200 to 1400 μmol m-2 s-1) and two levels of P fertilization (0 and 1 mM as KH2 PO4) for 160 days. The experimental design was a completely randomized in factorial arrangement (2 x 2), with 10 replications. The greatest growth in height and diameter was observed in plants fertilized with phosphorus and under high irradiance. Concerning the allocation of dry mass, plants under high irradiance invested more in root mass ratio and plants under low irradiance in leaf mass ratio. For foliar P content, the plants fertilized with P exhibited values 137 and 54% higher than the plants not fertilized with P, under high and low irradiance, respectively. The absence of P fertilization promoted intense reduction in the efficiency of electron transport, as demonstrated by the values of photochemical efficiency of photosystem II, and photosynthetic rates. The greatest biomass production and higher photosynthetic rates in plants fertilized with phosphorus and under higher irradiance suggest that O. pyramidale plants have appropriate functional mechanisms to show a better growth and physiological performance in open fields (high irradiance), common in forest plantations or environments in recovery process

Direct evidence for phosphorus limitation on Amazon forest productivity

The productivity of rainforests growing on highly weathered tropical soils is expected to be limited by phosphorus availability1. Yet, controlled fertilization experiments have been unable to demonstrate a dominant role for phosphorus in controlling tropical forest net primary productivity. Recent syntheses have demonstrated that responses to nitrogen addition are as large as to phosphorus2, and adaptations to low phosphorus availability appear to enable net primary productivity to be maintained across major soil phosphorus gradients3. Thus, the extent to which phosphorus availability limits tropical forest productivity is highly uncertain. The majority of the Amazonia, however, is characterized by soils that are more depleted in phosphorus than those in which most tropical fertilization experiments have taken place2. Thus, we established a phosphorus, nitrogen and base cation addition experiment in an old growth Amazon rainforest, with a low soil phosphorus content that is representative of approximately 60% of the Amazon basin. Here we show that net primary productivity increased exclusively with phosphorus addition. After 2 years, strong responses were observed in fine root (+29%) and canopy productivity (+19%), but not stem growth. The direct evidence of phosphorus limitation of net primary productivity suggests that phosphorus availability may restrict Amazon forest responses to CO2 fertilization4, with major implications for future carbon sequestration and forest resilience to climate change.The authors acknowledge funding from the UK Natural Environment Research Council (NERC), grant number NE/L007223/1. This is publication 850 in the technical series of the BDFFP. C.A.Q. acknowledges the grants from Brazilian National Council for Scientific and Technological Development (CNPq) CNPq/LBA 68/2013, CNPq/MCTI/FNDCT no. 18/2021 and his productivity grant. C.A.Q., H.F.V.C., F.D.S., I.A., L.F.L., E.O.M. and S.G. acknowledge the AmazonFACE programme for financial support in cooperation with Coordination for the Improvement of Higher Education Personnel (CAPES) and the National Institute of Amazonian Research as part of the grants CAPES-INPA/88887.154643/2017-00 and 88881.154644/2017-01. T.F.D. acknowledges funds from FundacAo de Amparo a Pesquisa do Estado de SAo Paulo (FAPESP), grant 2015/50488-5, and the Partnership for Enhanced Engagement in Research (PEER) programme grant AID-OAA-A-11-00012. L.E.O.C.A. thanks CNPq (314416/2020-0)

Biomassa, trocas gasosas e aspectos nutricionais de plantas jovens de ochroma pyramidale (cav. ex lamb) em resposta à fertilização nitrogenada e da interação fósforo e ambiente de luz

The plantation of forest species requires knowledge of their nutritional requirements and irradiance. This study investigated the effects of nitrate and ammonium fertilization and the interaction between phosphorus fertilization and irradiance levels in plants of Ochroma pyramidale. The experiment were conducted at the Laboratory of Plant Physiology and Biochemistry of the National Institute of Amazonian Research along 210 and 160 days for the experiment with N and P, respectively, under greenhouse conditions. The highest dry mass values were observed in plants fertilized with ammonium when compared with the control and plants fertilized with nitrate. For gas exchange, fertilization with ammonium promoted photosynthetic rates 106% and 19%, respectively, higher than those observed in the control plants and fertilized with nitrate. The phosphorus fertilization and the increase in irradiance contributed to the increase in dry mass of the whole plant and compartments. Photosynthetic rates were also higher in plants fertilized with phosphorus and submitted to higher irradiance. This information contributes to the understanding of the responses of young plants of Ochroma pyramidale to primary factors such as availability of N, P and irradiance and suggests new research that alow to study the physiological responses of this species to different proportion NO3-/ NH4+, different dosages of P, and the interaction between N and P, as well as other levels of irradiance, both in controlled conditions and in the field.O plantio de espécies florestais exige conhecimento dos seus requerimentos nutricionais e de irradiância. Neste trabalho investigou-se os efeitos da fertilização nítrica e amoniacal e da interação entre a fertilização fosfatada e níveis de irradiância em plantas de Ochroma pyramidale. Os experimentos foram conduzidos no Laboratório de Fisiologia e Bioquímica Vegetal do Instituto Nacional de Pesquisas da Amazônia sob regime de casa de vegetação, com duração de 210 e 160 dias, respectivamente, para os experimentos com N e P. Os maiores valores de massa seca foram observados nas plantas fertilizadas com amônio quando comparadas com o controle e com as plantas fertilizadas com nitrato. Para as trocas gasosas, a fertilização com amônio promoveu taxas fotossintéticas 106 e 19%, maiores que as observadas nas plantas do controle e nas fertilizadas com nitrato, respectivamente. A fertilização fosfatada e o aumento da irradiância contribuíram para o aumento na massa seca dos compartimentos e total das plantas. As taxas de fotossíntese também foram maiores nas plantas fertilizadas com fósforo e submetidas à maior irradiância. Essas informações contribuem para o entendimento das respostas de plantas jovens de O. pyramidale a fatores primários como disponibilidade de N, P e irradiância, e sugere novas investigações que permitam estudar as respostas fisiológicas dessa espécie a diferentes proporções NO3- / NH4+, a diferentes dosagens de P, e à interação entre N e P, assim como a outros níveis de irradiância, tanto em condições controladas como em condições de campo