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Progressive drought induced a gradual increase in non-structural carbohydrates in roots and leaves, slowing the drop in water status. The roots had an increase of 95 % compared to well-watered plants, while the leaves only increased by 21 %. Since Cenostigma pyramidale is a deciduous species, the non-structural carbohydrates are mainly found in the roots, which helps the plant survive the intense drought period. The ability to produce and control the distribution of non-structural carbohydrates (NSC) may be critical to the success of deciduous woody plants from seasonally dry tropical forests. Thus, our aim was to investigate how carbohydrate allocation occurs and the dynamics of water status during the pre-senescence leaf period. We performed a controlled experiment on progressive drought stress using Cenostigma pyramidale, and found that leaf relative water content decreased only under severe drought conditions (SVD), when soil water content was approximately 5%, three times less than well-hydrated plants, and foliar relative water content (RWC) was close to 35%. Gas exchange was maintained at a high level until the moderate drought stage (MD), with soil water content and RWC of 8% and 75%, respectively. Prior to leaf senescence, C. pyramidale maintained the net CO2 assimilation and intense production of NSC, which were stored mainly in the leaves (45%), and roots (44%), with only 11% in the stems. This increase in root NSC content during progressive drought levels suggests that this tissue may be the main storage site for NSC, which could allow the plant to survive the dry season, and also have reserves for leaf sprouting at the beginning of the next rainy season. The results suggest that studies involving carbon metabolism in woody species under stress should consider root tissue, as this is an important source of NSC during drought.

Exotic plants in semiarid region have developed strategies for efficient use or capture of resources. They have become invasive and outperform native species. To understand which factors could explain the success of invasive woody species in a semiarid region, several physiological traits were analyzed in young plants of two invasive and two native species exposed to different water availability. Invasive plants showed low leaf construction cost, high phosphorus and nitrogen contents, reduced loss of instantaneous energy use efficiency, and smaller specific leaf area when compared to native species. This strategy led to a higher biomass gain and a high root/shoot ratio in both water treatments. After rehydration, invasive plants showed faster recovery and higher rates of CO2 assimilation. This resilience is fundamental for species in semiarid regions, and also increase uptake of nutrients. Maintaining a high photosynthetic rate, whenever there is water availability is a strategy that increases the performance of the species in relation to biomass gain. The low leaf construction cost and the fast recovery of the photosynthetic metabolism of invasive plants after limiting water resources explains the success of these species, and suggests that their potential may increase under prolonged and severe drought seasons.

The evergreen C3 plant Calotropis procera is native to arid environments. Thus, it grows under high vapor pressure deficit (VPD), intense light, and severe drought conditions. We measured several ecophysiological traits in C. procera plants growing in semi-arid and seacoast environments to assess the attributes that support its photosynthetic performance under these contrasting conditions. Gas exchange analysis, primary metabolism content, nutrients, the antioxidant system, and leaf anatomy traits were measured under field conditions. In the semi-arid environment, C. procera was exposed to a prolonged drought season with a negative soil water balance during the 2 years of the study. Calotropis procera plants were exposed to a positive soil water balance only in the rainy season in the seacoast environment. The leaves of C. procera showed the same photosynthetic rate under high or low VPD, even in dry seasons with a negative soil water balance. Photosynthetic pigments, leaf sugar content, and the activity of antioxidant enzymes were increased in both places in the dry season. However, the anatomical adjustments were contrasting: while, in the semi-arid environment, mesophyll thickness increased in the driest year, in the seacoast environment, the cuticle thickness and trichome density were increased. The ability to maintain photosynthetic performance through the seasons would be supported by new leaves with different morpho-anatomical traits, with contrasting changes between semi-arid and seacoast environments. Furthermore, our results suggest that an efficient antioxidative system and leaf sugar dynamics can contribute to protecting the photosynthetic machinery even under severe drought.

Salinity may limit plant growth especially in arid and semiarid regions. Arbuscular mycorrhizal fungi (AMF) and the supply of inorganic phosphorus (Pi) could alleviate the negative effects of such stress by improvement in stomatal conductance, photosynthesis and biomass. The aim of this study is to evaluate the ecophysiological performance of Cenostigma pyramidale (Tul.) E. Gagnon & G. P. Lewis (Fabaceae) in a greenhouse under salinity conditions in combination with the supply of AMF and leaf Pi. The experiment was conducted in a factorial design considering two levels of salinity (+NaCl and -NaCl), two levels of AMF (+AMF and -AMF) and two levels of leaf Pi supply (+Pi and -Pi). The variables gas exchange, leaf primary metabolism, dry biomass and nutrients were measured. Plants with AMF under non-saline conditions presented a high photosynthesis and biomass. In saline conditions, AMF promoted lower decrease in photosynthesis, high shoot dry matter and low content of leaf and root Na+ and Cl-. Plants treated with leaf Pi increased biomass and photosynthetic pigments under both conditions and accumulated more Cl- in shoots under salinity conditions. When combined, AMF * Pi increased photosynthesis only in non-saline conditions. Plants under salinity conditions without AMF and Pi had higher decreases in gas exchange and high content of Cl- in roots. Therefore, C. pyramidale plants improved their metabolism under both growth conditions in the presence of AMF, Pi or a combination of both. However, the greatest increases in growth and tolerance to salinity occurred in the isolated presence of AMF.

The relationship between uptake and use of resources has always been highlighted among functional traits to explain the performance of invasive and native species. However, previous studies have shown that, under resource limitation, the species of both groups tend to have similar functional behavior. We measured a group of resource-use traits under controlled drought stress in Cenostigma microphyllum native to Caatinga of Brazil and the invasive species Calotropis procera that has a large occurrence in semiarid regions. The results showed that invasive well-watered plants always had higher CO2 assimilation rates and lower leaf construction costs than native plants, while stomatal conductance was similar. On the other hand, under water deficit conditions, the invasive plants tolerated more days of drought and showed higher root/shoot biomass ratio, leaf relative water content, lower leaf construction costs and payback time than the native species. Moreover, seven days after stress, the invasive plants displayed higher CO2 assimilation, photosynthetic nitrogen use efficiency, instantaneous efficiency of energy use and lower leaf construction costs compared with the native species. The ability to acquire and distribute resources among the different plant tissues at the right time seems to be a fundamental combination for the plants used in the experiment. Thus, a more acquisitive strategy is fundamental for having enough carbon to invest in the root biomass in C. procera under drought, which could contribute to maintain higher leaf water status for longer time compared with C. microphyllum.

In seasonal dry tropical forests, plants are subjected to severe water deficit, and the arbuscular mycorrhizal fungi (AMF) or inorganic phosphorus supply (Pi) can mitigate the effects of water deficit. This study aimed to assess the physiological performance of Poincianella pyramidalis subjected to water deficit in combination with arbuscular mycorrhizal fungi (AMF) and leaf inorganic phosphorus (Pi) supply. The experiment was conducted in a factorial arrangement of 2 water levels (+H2O and −H2O), 2 AMF levels (+AMF and −AMF) and 2 Pi levels (+Pi and −Pi). Leaf primary metabolism, dry shoot biomass and leaf mineral nutrients were evaluated. Inoculated AMF plants under well-watered and drought conditions had higher photosynthesis and higher shoot biomass. Under drought, AMF, Pi or AMF + Pi plants showed metabolic improvements in photosynthesis, leaf biochemistry and higher biomass compared to the plants under water deficit without AMF or Pi. After rehydration, those plants submitted to drought with AMF, Pi or AMF + Pi showed a faster recovery of photosynthesis compared to treatment under water deficit without AMF or Pi. However, plants under the drought condition with AMF showed a higher net photosynthesis rate. These findings suggest that AMF, Pi or AMF + Pi increase the drought tolerance in P. pyramidalis, and AMF associations under well-watered conditions increase shoot biomass and, under drought, promoted faster recovery of photosynthesis.

The study aimed at assessing whether there is association between arbuscular mycorrhizal fungi (AMF) and two woody species from a seasonal dry tropical forest, Poincianella pyramidalis and Cnidoscolus quercifolius, besides the occurrence of an increase in biomass under different availability of phosphorus (P) in the soil. The experimental design was completely randomized, with a factorial design with two mycorrhizal levels [inoculated (+AMF) and control (−AMF)] × six phosphorus levels (3, 9, 15, 21, 27, 33 mg dm−3). The presence of mycorrhizal structures, mycorrhizal growth, mycorrhizal efficiency, leaf relative water content (RWC) and gas exchange were evaluated. +AMF plants of both species had mycorrhizal structures, while −AMF showed no structures. In P. pyramidalis, +AMF plants had benefits with increasing phosphorus level, while −AMF plants had increases biomass only at the P9 level if compared to the P3-AMF level. The total leaf area was correlated with total dry weight (TDW) in +AMF and −AMF plants. However, +AMF plants had more responses in RWC. In C. quercifolius, +AMF and −AMF plants did not differ in RWC and showed reductions in gas exchange with increased phosphorus level. However, these reductions were lower in +AMF plants, besides having a better performance over −AMF plants. The growth and mycorrhizal efficiency were higher at the P15 level, and relationship between total leaf area and TDW were significant only in +AMF plants. Thus, both species perform association with AMF and show increases in growth. The concentrations of phosphorus in the soil for P. pyramidalis (33 mg dm−3) and C. quercifolius (15 mg dm−3) are indicated for increased effectiveness of mycorrhization, promote increases in gas exchange and growth in +AMF plants.

Plants suffer recurrent cycles of water deficit in semiarid regions and have several mechanisms to tolerate low water availability. Thus, arbuscular mycorrhizal fungi (AMF) can alleviate deleterious effects of stress. In this study, Cynophalla flexuosa plants, a woody evergreen species from semiarid, when associated with AMF were exposed to two consecutive cycles of water deficit. Leaf primary metabolism, specific leaf area (SLA), leaf construction cost (CC) and photosynthetic energy use efficiency (PEUE) were measured. The maximum stress occurred on seven days (cycle 1) and ten days (cycle 2) after suspending irrigation (photosynthesis close to zero). The rehydration was performed for three days after each maximum stress. In both cycles, plants submitted to water deficit showed reduced gas exchange and leaf relative water content. However, Drought + AMF plants had significantly larger leaf relative water content in cycle 2. At cycle 1, the SLA was larger in non-inoculated plants, while CC was higher in inoculated plants. At cycle 2, Drought + AMF treatment had lower CC and large SLA compared to control, and high PEUE compared to Drought plants. These responses suggest AMFs increase tolerance of C. flexuosa to recurrent water deficit, mainly in cycle 2, reducing the CC, promoting the improvement of SLA and PEUE, leading to higher photosynthetic area. Thus, our result emphasizes the importance of studies on recurrence of water deficit, a common condition in semiarid environments.