(1) One strategy for plants to optimise stomatal function is to open and close their stomata quickly in response to environmental signals. It is generally assumed that small stomata can alter aperture faster than large stomata. (2) We tested the hypothesis that species with small stomata close faster than species with larger stomata in response to darkness by comparing rate of stomatal closure across an evolutionary range of species including ferns, cycads, conifers and angiosperms under controlled ambient conditions (380ppm CO2; 20.9% O2). (3) The two species with fastest half-closure time and the two species with slowest half-closure time had large stomata while the remaining three species had small stomata, implying that closing rate was not correlated with stomatal size in these species. Neither was response time correlated with stomatal density, phylogeny, functional group or life strategy. (4) Our results suggest that past atmospheric CO2 concentration during time of taxa diversification may influence stomatal response time. We show that species which last diversified under low or declining atmospheric CO2 concentration close stomata faster than species that last diversified in a high CO2 world. Low atmospheric [CO2] during taxa diversification may have placed a selection pressure on plants to accelerate stomatal closing to maintain adequate internal CO2 and optimise water use efficiency.

Studies have indicated that plant stomatal conductance (g_s) decreases in response to elevated atmospheric CO₂, a phenomenon of significance for the global hydrological cycle. However, g_s increases across certain CO₂ ranges have been predicted by optimization models. The aim of this work was to demonstrate that under certain environmental conditions, g_s can increase in response to elevated CO₂. Using (1) an extensive, up-to-date synthesis of g_s responses in free air CO₂ enrichment (FACE)experiments, (2) in situ measurements across four biomes showing dynamic g_s responses to a CO₂ rise of ~50 ppm (characterizing the change in this greenhouse gas over the past three decades) and (3) a photosynthesis–stomatal conductance model, it is demonstrated that g_s can in some cases increase in response to increasing atmospheric CO₂. Field observations are corroborated by an extensive synthesis of g_s responses in FACE experiments showing that 11.8 % of g_s responses under experimentally elevated CO₂ are positive. They are further supported by a strong data-model fit (r² = 0.607) using a stomatal optimization model applied to the field g_s dataset. A parameter space identified in the Farquhar–Ball–Berry photosynthesis–stomatal conductance model confirms field observations of increasing g_s under elevated CO₂ in hot dry conditions. Contrary to the general assumption, positive g_s responses to elevated CO₂, although relatively rare, are a feature of woody taxa adapted to warm, low-humidity conditions, and this response is also demonstrated in global simulations using the Community Land Model (CLM4). The results contradict the over-simplistic notion that global vegetation always responds with decreasing g_s to elevated CO₂, a finding that has important implications for predicting future vegetation feedbacks on the hydrological cycle at the regional level.

Fungal endophytes have great potential as biocontrol and biofertilisation agents for food crops, and it is important to understand and optimise the cultural conditions for endophyte emergence and growth. A range of commercial culture media were tested for their effect on endophyte recovery from the roots of their host ( Hordeum murinum ), and for their subsequent growth and sporulation. Furthermore, a medium composed of sterile or filtered whole plant extract (WPE) was tested at various dilutions both alone and in combination with one of the commercial media. It was found that there were significant differences between the media in endophyte recovery, endophyte mycelial growth and time to sporulation. A significantly greater number of different endophytes were recovered from roots on the malt extract plus WPE medium than any of the other media tested here. Sabouraud medium gave the greatest mean radial growth of endophyte fungal mycelia after 35 days. The cultures growing on the WPE media took over five times longer to sporulate than all other media. Results indicate that different media are suitable either for the initial recovery and isolation of fungal root endophytes or for increasing fungal biomass and inducing earlier sporulation. The experimental endophytes used here have previously been shown to have biocontrol and biofertilisation benefits for barley cultivars, so our findings have important implications for the development and commercialisation of endophyte inocula.

High energy weather events are often expected to play a substantial role in biotic community dynamics and large scale diversity patterns but their contribution is hard to prove. Currently, observations are limited to the documentation of accidental records after the passing of such events. A more comprehensive approach is synthesising weather events in a location over a long time period, ideally at a high spatial resolution and on a large geographic scale. We provide a detailed overview on how to generate hurricane exposure data at a meso-climate level for a specific region. As a case study we modelled landscape hurricane exposure in Cusuco National Park (CNP), Honduras with a resolution of 50 m×50 m patches. We calculated actual hurricane exposure vulnerability site scores (EVVS) through the combination of a wind pressure model, an exposure model that can incorporate simple wind dynamics within a 3-dimensional landscape and the integration of historical hurricanes data. The EVSS was calculated as a weighted function of sites exposure, hurricane frequency and maximum wind velocity. Eleven hurricanes were found to have affected CNP between 1995 and 2010. The highest EVSS’s were predicted to be on South and South-East facing sites of the park. Ground validation demonstrated that the South-solution (i.e. the South wind inflow direction) explained most of the observed tree damage (90% of the observed tree damage in the field). Incorporating historical data to the model to calculate actual hurricane exposure values, instead of potential exposure values, increased the model fit by 50%.

IPCC predictions for Honduras indicate that temperature will increase by up to 3–6°C and precipitation will decrease by up to 7–13% by the year 2050. To better understand how fern and lycophyte communities might be affected by climate change, we comprehensively surveyed the community compositions of ferns and lycophytes at Celaque National Park, the highest mountain in Honduras. We surveyed a total of 80 20 × 20 m²plots along an altitudinal gradient of 1249–2844 m a.s.l., identifying all species and estimating their abundances. We recorded a total of 11,098 individuals from 160 species and 61 genera. Community composition was strongly influenced by changes in altitude, precipitation and the abundance of bryophytes (a proxy for air humidity). Of the 160 species, 63 are expected, under a RCP2.6 scenario for the year 2050, to shift their range fully or partially above the maximum altitude of the mountain. Of these, 65.1% are epiphytes. We found that species with narrow altitudinal ranges at high altitudes were more at risk. Our study indicated that conservation efforts should prioritise higher altitudinal sites, focusing particularly on preserving the vulnerable epiphytic fern species, which are likely to be at greater risk.

Main conclusion: Our study demonstrated that the species respond non-linearly to increases in CO₂ concentration when exposed to decadal changes in CO₂, representing the year 1987, 2025, 2051, and 2070, respectively. There are several lines of evidence suggesting that the vast majority of C3 plants respond to elevated atmospheric CO₂ by decreasing their stomatal conductance (g_s). However, in the majority of CO₂ enrichment studies, the response to elevated CO₂ are tested between plants grown under ambient (380–420 ppm) and high (538–680 ppm) CO₂ concentrations and measured usually at single time points in a diurnal cycle. We investigated g_s responses to simulated decadal increments in CO₂ predicted over the next 4 decades and tested how measurements of g_s may differ when two alternative sampling methods are employed (infrared gas analyzer [IRGA] vs. leaf porometer). We exposed Populus tremula, Popolus tremuloides and Sambucus racemosa to four different CO₂ concentrations over 126 days in experimental growth chambers at 350, 420, 490 and 560 ppm CO₂; representing the years 1987, 2025, 2051, and 2070, respectively (RCP4.5 scenario). Our study demonstrated that the species respond non-linearly to increases in CO₂ concentration when exposed to decadal changes in CO₂. Under natural conditions, maximum operational g_s is often reached in the late morning to early afternoon, with a mid-day depression around noon. However, we showed that the daily maximum g_s can, in some species, shift later into the day when plants are exposed to only small increases (70 ppm) in CO₂. A non-linear decreases in g_s and a shifting diurnal stomatal behavior under elevated CO₂, could affect the long-term daily water and carbon budget of many plants in the future, and therefore alter soil–plant–atmospheric processes.