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Summary: In severely phosphorus (P)‐impoverished environments, plants have evolved to use P very efficiently. Yet, it is unclear how P allocation in leaves contributes to their photosynthetic P‐use efficiency (PPUE) and position along the leaf economics spectrum (LES). We address this question in 10 species of Banksia and Hakea, two highly P‐efficient Proteaceae genera.We characterised traits in leaves of Banksia and Hakea associated with the LES: leaf mass per area, light‐saturated photosynthetic rates, P and nitrogen concentrations, and PPUE. We also determined leaf P partitioning to five biochemical fractions (lipid, nucleic acid, metabolite, inorganic and residual P) and their possible association with the LES.For both genera, PPUE was negatively correlated with fractional allocation of P to lipids, but positively correlated with that to metabolites. For Banksia only, PPUE was negatively correlated with residual P, highlighting a strategy contrasting to that of Hakea. Phosphorus‐allocation patterns significantly explained PPUE but were not linked to the resource acquisition vs resource conservation gradient defined by the LES.We conclude that distinct P‐allocation patterns enable species from different genera to achieve high PPUE and discuss the implications of different P investments. We surmise that different LES axes representing different ecological strategies coexist in extremely P‐impoverished environments. [ABSTRACT FROM AUTHOR]

Summary: Nonmycorrhizal cluster root‐forming species enhance the phosphorus (P) acquisition of mycorrhizal neighbours in P‐impoverished megadiverse systems. However, whether mycorrhizal plants facilitate the defence of nonmycorrhizal plants against soil‐borne pathogens, in return and via their symbiosis, remains unknown.We characterised growth and defence‐related compounds in Banksia menziesii (nonmycorrhizal) and Eucalyptus todtiana (ectomycorrhizal, ECM) seedlings grown either in monoculture or mixture in a multifactorial glasshouse experiment involving ECM fungi and native oomycete pathogens.Roots of B. menziesii had higher levels of phytohormones (salicylic and jasmonic acids, jasmonoyl‐isoleucine and 12‐oxo‐phytodienoic acid) than E. todtiana which further activated a salicylic acid‐mediated defence response in roots of B. menziesii, but only in the presence of ECM fungi. We also found that B. menziesii induced a shift in the defence strategy of E. todtiana, from defence‐related secondary metabolites (phenolic and flavonoid) towards induced phytohormone response pathways.We conclude that ECM fungi play a vital role in the interactions between mycorrhizal and nonmycorrhizal plants in a severely P‐impoverished environment, by introducing a competitive component within the facilitation interaction between the two plant species with contrasting nutrient‐acquisition strategies. This study sheds light on the interplay between beneficial and detrimental soil microbes that shape plant–plant interaction in severely nutrient‐impoverished ecosystems. [ABSTRACT FROM AUTHOR]

Low temperatures largely determine the geographic limits of plant species by reducing survival and growth. Inter-specific differences in the geographic distribution of mangrove species have been associated with cold tolerance, with exclusively tropical species being highly cold-sensitive and subtropical species being relatively cold-tolerant. To identify species-specific adaptations to low temperatures, we compared the chilling stress response of two widespread Indo-West Pacific mangrove species from Rhizophoraceae with differing latitudinal range limits— Bruguiera gymnorhiza (L.) Lam. ex Savigny (subtropical range limit) and Rhizophora apiculata Blume (tropical range limit). For both species, we measured the maximum photochemical efficiency of photosystem II (F v/ F m) as a proxy for the physiological condition of the plants and examined gene expression profiles during chilling at 15 and 5 °C. At 15 °C, B. gymnorhiza maintained a significantly higher F v/ F m than R. apiculata. However, at 5 °C, both species displayed equivalent F v/ F m values. Thus, species-specific differences in chilling tolerance were only found at 15 °C, and both species were sensitive to chilling at 5 °C. At 15 °C, B. gymnorhiza downregulated genes related to the light reactions of photosynthesis and upregulated a gene involved in cyclic electron flow regulation, whereas R. apiculata downregulated more RuBisCo-related genes. At 5 °C, both species repressed genes related to CO2 assimilation. The downregulation of genes related to light absorption and upregulation of genes related to cyclic electron flow regulation are photoprotective mechanisms that likely contributed to the greater photosystem II photochemical efficiency of B. gymnorhiza at 15 °C. The results of this study provide evidence that the distributional range limits and potentially the expansion rates of plant species are associated with differences in the regulation of photosynthesis and photoprotective mechanisms under low temperatures. [ABSTRACT FROM AUTHOR]

Background and Aims Soils in south-western Australia are severely phosphorus (P) impoverished, and plants in this region have evolved a variety of P-acquisition strategies. Phosphorus acquisition by Adenanthos cygnorum (Proteaceae) is facilitated by P-mobilizing neighbours which allows it to extend its range of habitats. However, we do not know if other Adenanthos species also exhibit a strategy based on facilitation for P acquisition in P-impoverished environments. Methods We collected leaf and soil samples of Adenanthos barbiger , A. cuneatus , A. meisneri, A. obovatus , A. sericeus and Adenanthos sp. Whicher Range (G.J. Keighery 9736) growing in their natural habitats at different locations within the severely P-limited megadiverse environment of south-western Australia. Hydroponic experiments were conducted to collect the carboxylates exuded by cluster roots. Pot experiments in soil were carried out to measure rhizosheath phosphatase activity. Key Results We found no evidence for facilitation of P uptake in any of the studied Adenanthos species. Like most Proteaceae, A. cuneatus , A. meisneri , A. obovatus , A. sericeus and Adenanthos sp. Whicher Range (G.J. Keighery 9736) expressed P-mining strategies, including the formation of cluster roots. Cluster roots of A. obovatus were less effective than those of the other four Adenanthos species. In contrast to what is known for most Proteaceae, we found no cluster roots for A. barbiger. This species probably expressed a post-fire P-acquisition strategy. All Adenanthos species used P highly efficiently for photosynthesis, like other Proteaceae in similar natural habitats. Conclusions Adenanthos is the first genus of Proteaceae found to express multiple P-acquisition strategies. The diversity of P-acquisition strategies in these Proteaceae, coupled with similarly diverse strategies in Fabaceae and Myrtaceae, demonstrates that caution is needed in making family- or genus-wide extrapolations about the strategies exhibited in severely P-impoverished megadiverse ecosystems. [ABSTRACT FROM AUTHOR]

Summary: Leaf phosphorus (P) comprises four major fractions: inorganic phosphate (Pi), nucleic acids, phospholipids, P‐containing metabolites and a residual fraction. In this review paper, we investigated whether allocation of P fractions varies among groups of terrestrial vascular plants, and is indicative of a species' strategy to use P efficiently. We found that as leaf total P concentration increases, the Pi fraction increases the most, without a plateau, while other fractions plateau. Variability of the concentrations of leaf P fractions is greatest among families > species(family) > regions > plant life forms. The percentage of total P allocated to nucleic acid‐P (20–35%) and lipid‐P (14–34%) varies less among families/species. High photosynthetic P‐use efficiency is associated with low concentrations of all P fractions, and preferential allocation of P to metabolite‐P and mesophyll cells. Sequential resorption of P from senescing leaves starts with Pi, followed by metabolite‐P, and then other organic P fractions. Allocation of P to leaf P fractions varies with season. Leaf phytate concentrations vary considerably among species, associated with variation in photosynthesis and defence. Plasticity of P allocation to its fractions is important for acclimation to low soil P availability, and species‐specific P allocation is needed for co‐occurrence with other species. [ABSTRACT FROM AUTHOR]

Desiccation-tolerant (DT) plants can withstand dehydration to less than 0.1 g H2O g−1 dry weight. The mechanism for whole-plant recovery from severe dehydration is still not clear, especially for woody DT plants. In the present study, we evaluated the desiccation tolerance and mechanism of recovery for a potentially new woody resurrection plant Paraboea rufescens (Gesneriaceae). We monitored the leaf water status, leaf gas exchange, chlorophyll fluorescence and root pressure of potted P. rufescens during dehydration and rehydration, and we investigated the water content and chlorophyll fluorescence of P. rufescens leaves in the field during the dry season. After re-watering from a severely dehydrated state, leaf maximum quantum yield of photosystem II of P. rufescens quickly recovered to well-watered levels. Leaf water status and leaf hydraulic conductance quickly recovered to well-watered levels after re-watering, while leaf gas exchange traits also trended to recovery, but at a slower rate. The maximum root pressure in rehydrated P. rufescens was more than twice in well-watered plants. Our study identified P. rufescens as a new DT woody plant. The whole-plant recovery of P. rufescens from extreme dehydration is potentially associated with an increase of root pressure after rehydration. These findings provide insights into the mechanisms of recovery of DT plants from dehydration. [ABSTRACT FROM AUTHOR]

Tropical forests play important roles in global carbon cycling. Tree-ring analysis can provide important information for understanding long-term trends in carbon-fixation capacity under climate change. However, tree-ring studies in tropical regions are limited. We carried out a tree-ring analysis to investigate the dendrochronological potential of the tropical forest tree Choerospondias axillaris (Anacardiaceae) in east-central Thailand. Our study focused on growth-climate relationships and long-term growth trends. A chronology was constructed covering the period from 1932 to 2019. The tree-ring width index of C. axillaris was positively correlated with precipitation in June, July, and October. Furthermore, growth of C. axillaris was positively correlated with the Standardized Precipitation-Evapotranspiration Index (SPEI) from July to October, indicating that growth of C. axillaris is mainly limited by moisture availability in the late monsoon season. Moving correlation analysis further revealed the consistency and temporal stability of the relationship of tree growth with monsoon season precipitation and SPEI during the period under study. There was a significant increasing trend in long-term growth from 1932 to 2002 (slope = 0.017, p < 0.001); however, long-term growth decreased from 2003 to 2019 (slope = −0.014, p < 0.001). Our study provides important insight into the growth-climate correlations of a broad-leaved tree species in a dry evergreen forest in tropical Asia. [ABSTRACT FROM AUTHOR]

Background and Aims Phosphorus (P) and nitrogen (N) are essential nutrients that frequently limit primary productivity in terrestrial ecosystems. Efficient use of these nutrients is important for plants growing in nutrient-poor environments. Plants generally reduce foliar P concentration in response to low soil P availability. We aimed to assess ecophysiological mechanisms and adaptive strategies for efficient use of P in Banksia attenuata (Proteaceae), naturally occurring on deep sand, and B. sessilis , occurring on shallow sand over laterite or limestone, by comparing the allocation of P among foliar P fractions. Methods We carried out pot experiments with slow-growing B. attenuata , which resprouts after fire, and faster growing opportunistic B. sessilis , which is killed by fire, on substrates with different P availability using a randomized complete block design. We measured leaf P and N concentrations, photosynthesis, leaf mass per area, relative growth rate and P allocated to major biochemical fractions in B. attenuata and B. sessilis. Key Results The two species had similarly low foliar total P concentrations, but distinct patterns of P allocation to P-containing fractions. The foliar total N concentration of B. sessilis was greater than that of B. attenuata on all substrates. The foliar total P and N concentrations in both species decreased with decreasing P availability. The relative growth rate of both species was positively correlated with concentrations of both foliar nucleic acid P and total N, but there was no correlation with other P fractions. Faster growing B. sessilis allocated more P to nucleic acids than B. attenuata did, but other fractions were similar. Conclusions The nutrient allocation patterns in faster growing opportunistic B. sessilis and slower growing B. attenuata revealed different strategies in response to soil P availability which matched their contrasting growth strategy. [ABSTRACT FROM AUTHOR]