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In no-till cropping systems, banding of phosphorus (P) fertiliser at seeding results in low use efficiency due to chemical reactions in soil. Foliar P has the potential to allow grain producers to respond tactically with P application after sowing when P supply from soil and fertiliser is not meeting crop demand. The objective of this study was to evaluate the effectiveness of foliar P on wheat grain yield, grain quality, biomass yield, P uptake and P use efficiency indices. Nine field experiments were conducted to investigate the response of wheat to foliar P. Three rates of P, 0, 2.5 and 5.0 kg/ha, as phosphoric acid (H3PO4 85%) were applied to wheat at three different growth stages: first tiller emergence (Z21), first node detection (Z31) and flag leaf emergence (Z39). Grain yield responses ranging from 176 kg/ha to 505 kg/ha to foliar-applied P were observed in six out of nine experiments. The percent grain yield response to foliar P was negatively related to the P buffering index (PBI, 0–10 cm soil depth), which is attributed to greater sorption by soil of the foliar P at the higher PBI levels. Mean agronomic efficiency (AE) across the experiments was 111 kg/kg P but reached up to 232 kg/kg P. It was also evident that foliar P has the potential to improve P concentration in shoots and grains and increase P uptake but with no or minimal effect on grain quality. Our results suggest that a combination of tissue testing at the seedling stage and soil P buffering can be used to guide when foliar P application is likely to increase grain yield in wheat. [ABSTRACT FROM AUTHOR]

Tree species establish mycorrhizal associations with both ectomycorrhizal (EM) and arbuscular mycorrhizal fungi (AM), which play crucial roles in facilitating plant phosphorus (P) acquisition. However, little attention has been given to the effects of EM and AM species on soil P dynamics and the underlying mechanisms in subtropical forests, where P availability is typically low. To address this knowledge gap, we selected two EM species (Pinus massoniana - PM and Castanopsis carlesii - CC) and two AM species (Cunninghamia lanceolata - Chinese fir, CF and Michelia macclurei - MM) in a common garden established in 2012 in subtropical China. We investigated soil properties (e.g., pH, soil organic carbon, total nitrogen, and dissolved organic nitrogen), soil P fractions, phospholipid fatty acids (PLFAs), enzyme activities, foliar manganese (Mn) concentration, and foliar nutrients and stoichiometry. Our findings revealed that soils hosting EM species had higher levels of resin P, NaHCO3-Pi, extractable Po, total P, and a greater percentage of extractable Po to total P compared to soils with AM species. These results indicate that EM species enhance soil P availability and organic P accumulation in contrast to AM species. Moreover, EM species exhibited higher P return to soil (indicated by higher foliar P concentrations) when compared to AM species, which partly explains higher P accumulation in soils with EM species. Additionally, resin P showed a positive correlation with acid phosphatase (ACP) activity, whereas no correlation was found with foliar Mn concentration, which serves as a proxy for the mobilization of sorbed soil P. Such findings indicate that organic P mineralization has a more substantial impact than inorganic P desorption in influencing P availability in soils hosting both EM and AM species. In summary, our study contributes to a more comprehensive understanding of the effects of mycorrhizal associations on soil P accumulation in subtropical forests and provide valuable insights into plant-soil interactions and their role in P cycling in regions with limited P availability. [ABSTRACT FROM AUTHOR]

The early spring is a seasonal high-light "window" for new leaf growth and photosynthetic carbon capture by the shade-tolerant evergreen understory plants. However, it remains unclear how light regulates the source-sink relationship between rhizome (RO), mature leaf (ML), and immature leaf (IL) during Coptis chinensis leaf expansion. Understanding this relationship is essential to reducing RO reserve degradation and ultimately promote RO biomass accumulation. The plants grew in an artificial climate chamber with low (50 μmol m-2 s-1) and relatively high (200 μmol m-2 s-1) light intensity treatments. Leaf fluorescence, foliar phosphorus (P) fractions, soluble sugars, starch, total P, and alkaloid concentrations in ILs, MLs, and RO were measured, and 13C labeling was used to indicate the direction of photosynthetic carbon flow between organs. The plants grown under high light intensity had higher levels of starch in RO and higher RO biomass at the end of the year compared to those grown under low light intensity. The photosystemII (PSII) operating efficiency [Y(II)], relative electron transport rate (rETR), and photochemical quenching (qP), as well as sucrose and glucose, in ILs andMLs under relatively high light, was higher than those under low light. The glucose and starch concentrations in ILs at 35 d was significantly higher than that at 15 d when plants were under 200 μmol m-2 s-1, while they were not significantly changed and remained low at 50 μmol m-2 s-1. The 13C was detected in the RO when plants were grown at 200 μmol m-2 s-1, regardless of ILs and MLs 13C labeling, while no 13C was detected in the ROwhen plantswere under 50 μmol m-2 s-1. Additionally, the proportion of photosynthetic transport from ILs to MLs was significantly higher than that fromMLs to ILs under the 50-μmol m-2 s-1 limit. Total P concentration in ILs was lower under relatively high light, but there was no difference in nucleic acid P concentration in ILs under the two light intensity treatments. The alkaloid concentration in RO was lower under 200 μmol m-2 s-1 than that under 50 μmol m-2 s-1. We propose that relatively high light reduces the need for carbohydrates and P stored in the RO to support IL growth by (1) accelerating the sink-to-source transition in ILs, which inhibits the use of reserves in the RO; (2) using energy from MLs to support IL growth, thereby reducing RO reserve consumption, and (3) reducing the demand for P by investing less in the development of photosynthetic machinery. Furthermore, under low light, MLs serve as a sink and rely on other organs for support, directly or indirectly exacerbating the reserves lost in the RO. [ABSTRACT FROM AUTHOR]

In tropical mountains, trees are the dominant life form from sea level to above 4,000-m altitude under highly variable thermal conditions (range of mean annual temperatures: <8 to >28°C). How light-saturated net photosynthesis of tropical trees adapts to variation in temperature, atmospheric CO concentration, and further environmental factors, that change along elevation gradients, is not precisely known. With gas exchange measurements in mature trees, we determined light-saturated net photosynthesis at ambient temperature (T) and [CO] ( A) of 40 tree species from 21 families in tropical mountain forests at 1000-, 2000-, and 3000-m elevation in southern Ecuador. We tested the hypothesis that stand-level averages of A and leaf dark respiration ( R) per leaf area remain constant with elevation. Stand-level means of A were 8.8, 11.3, and 7.2 μmol CO m s; those of R 0.8, 0.6, and 0.7 μmol CO m s at 1000-, 2000-, and 3000-m elevation, respectively, with no significant altitudinal trend. We obtained coefficients of among-species variation in A and R of 20-53% ( n = 10-16 tree species per stand). Examining our data in the context of a pan-tropical A data base for mature tropical trees (c. 170 species from 18 sites at variable elevation) revealed that area-based A decreases in tropical mountains by, on average, 1.3 μmol CO m s per km altitude increase (or by 0.2 μmol CO m s per K temperature decrease). The A decrease occurred despite an increase in leaf mass per area with altitude. Local geological and soil fertility conditions and related foliar N and P concentrations considerably influenced the altitudinal A patterns. We conclude that elevation is an important influencing factor of the photosynthetic activity of tropical trees. Lowered A together with a reduced stand leaf area decrease canopy C gain with elevation in tropical mountains. [ABSTRACT FROM AUTHOR]

Foliar respiration is a major component of ecosystem respiration, yet extrapolations are often uncertain in tropical forests because of indirect estimates of leaf area index (LAI). A portable tower was used to directly measure LAI and night-time foliar respiration from 52 vertical transects throughout an old-growth tropical rain forest in Costa Rica. In this study, we (1) explored the effects of structural, functional and environmental variables on foliar respiration; (2) extrapolated foliar respiration to the ecosystem; and (3) estimated ecosystem respiration. Foliar respiration temperature response was constant within plant functional group, and foliar morphology drove much of the within-canopy variability in respiration and foliar nutrients. Foliar respiration per unit ground area was 3.5 ± 0.2 µmol CO2 m−2 s−1, and ecosystem respiration was 9.4 ± 0.5 µmol CO2 m−2 s−1[soil = 41%; foliage = 37%; woody = 14%; coarse woody debris (CWD) = 7%]. When modelled with El Niño Southern Oscillation (ENSO) year temperatures, foliar respiration was 9% greater than when modelled with temperatures from a normal year, which is in the range of carbon sink versus source behaviour for this forest. Our ecosystem respiration estimate from component fluxes was 33% greater than night-time net ecosystem exchange for the same forest, suggesting that studies reporting a large carbon sink for tropical rain forests based solely on eddy flux measurements may be in error. [ABSTRACT FROM AUTHOR]

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