Biology subjects

Robson, T. M.

Publications and source records attributed to Robson, T. M..

4 recordsLinked to original sources

bioRxiv2019

The contribution of PIP2-type aquaporins to photosynthesis in response to increased vapour pressure deficit

Roles of three different plasma membrane aquaporins (PIPs) in leaf-level gas exchange of Arabidopsis thaliana were examined using single, double and triple knockout mutants and compared to the Columbia-0 wild type (WT) plants. Since multiple Arabidopsis PIPs are implicated in conducting carbon dioxide across membranes, we focused on identifying whether the examined isoforms affect photosynthesis, either mediated through the control of stomatal conductance to water vapour (gs) or mesophyll conductance of CO2 (gm) or a combination of both. In two separate studies, we grew Arabidopsis plants in a low humidity environment and under high humidity conditions. We found that the contribution of functional PIPs to gs was larger under conditions of low air humidity when the evaporative demand was high, whereas any effect of lacking PIP function was minimal under higher humidity conditions. The pip2;4 knockout mutants had 44% higher gs than the WT under low humidity conditions, which in turn resulted in an increased photosynthetic rate (Anet). AtPIP2;4 is thus likely to be involved in maintaining a positive water balance and high water use efficiency through mediation of transmembrane water flow. The lack of functional AtPIP2;5 on the other hand did not affect gs, but reduced gm indicating a possible role in regulating CO2 membrane permeability. This potential regulatory function was indeed confirmed by subsequent stopped flow measurements of yeast expressing AtPIP2;5.

plant biology↗

bioRxiv2019

Understory light quality affects leaf pigments and leaf phenology in different plant functional types

Understory plant species take on different functional strategies, whereby some exploit periods of available light in springtime before the canopy closes, and others also benefit from sunlight later in autumn when the canopy opens again. These strategies involve understory species coordinating phenological events to pre-empt canopy leaf out and to extend their growing season beyond canopy leaf senescence, meanwhile accumulating photo-protective pigments which mitigate periods of high-light exposure. Canopy closure brings shade to the understory, but also causes drastic changes in light quality. Whilst many experiments manipulating spectral quality have revealed understory plant responses to the changing R:FR ratio in shade, effect of the blue and UV regions have been examined very little. We installed filters attenuating short wavelength regions of the solar spectrum in a forest understory in southern Finland, creating the following treatments: a transparent control filter, and filters attenuating UV radiation < 350 nm, all UV radiation, and both UV and blue light. In eight understory species, representing different plant functional types, we repeatedly assessed leaf optical properties to obtain epidermal flavonol and anthocyanin contents from leaf emergence in spring to leaf senescence in autumn, during both 2017 and 2018. Flavonols responded more to seasonal changes in light quality in relatively light-demanding species than in shade-tolerant and wintergreen species; and were particularly responsive to blue light. However, anthocyanins were largely unaffected by our filter treatments, suggesting that other cues such as cold temperatures govern their seasonal variation. UV radiation only accelerated leaf senescence in Acer platanoides seedlings, but blue light accelerated leaf senescence in all species measured apart from Quercus robur. In summary, seasonal changes in understory solar radiation in the blue and UV regions affected leaf pigments and leaf phenology; particularly for more light-demanding species. An increase in canopy duration under climate change will extend the period of shade in the understory, with consequences for the spectral cues available to understory plants. The resultant reduction in blue and UV radiation in shade, could delay leaf senescence in the understory even further.

plant biology↗

bioRxiv2019

Greater capacity to exploit warming temperatures in northern populations of European beech is partly driven by delayed leaf senescence

One of the most widespread consequences of climate change is the disruption of trees phenological cycles. The extent to which tree phenology varies with local climate is largely genetically determined, and while a combination of temperature and photoperiodic cues are typically found to trigger bud burst (BB) in spring, it has proven harder to identify the main cues driving leaf senescence (LS) in autumn. We used 925 individual field-observations of BB and LS from six Fagus sylvatica provenances, covering the range of environmental conditions found across the species distribution, to: (i) estimate the dates of BB and LS of these provenances; (ii) assess the main drivers of LS; and (iii) predict the likely variation in the growing season length (GSL; defined by BB and LS timing) across populations under current and future climate scenarios. To this end, we first calibrated linear mixed-effects models for LS as a function of temperature, insolation and BB date. Secondly, we calculated the GSL for each provenance as the number of days between BB and LS. We found that: i) there were larger differences among provenances in the date of LS than in the date of BB; ii) the temperature through September, October and November was the main determinant of LS in beech, although covariation of temperature with daily insolation and precipitation-related variables suggests that all three variables may affect LS timing; and iii) GSL was predicted to increase in northern beech provenances and to shrink in populations from the core and the southern range under climate change. Consequently, the large differences in GSL across beech range in the present climate are likely to decrease under future climates where rising temperatures will alter the relationship between BB and LS, with northern populations increasing productivity by extending their growing season to take advantage of warmer conditions.

ecology↗

bioRxiv2018

Blue light advances bud burst in branches of three temperate deciduous tree species under short-day conditions

During spring, utilising multiple cues allow temperate tree species to coordinate their bud burst and leaf out, at the right moment to capitalise on favourable conditions for photosynthesis. Whilst the effect of blue light (400-500nm) has been shown to increase percentage bud burst of axillary shoots of Rosa sp, the effects of blue light on spring-time bud burst of temperate deciduous tree species has not previously been reported. We tested the hypotheses that blue light would advance spring bud burst in temperate tree species, and that late-successional species would respond more than early-successional species, whos bud burst is primarily determined by temperature. The bud development of Alnus glutinosa, Betula pendula, and Quercus robur branches, cut from dormant trees, was monitored under two light treatments of equal photosynthetically active radiation (PAR, 400-700 nm) and temperature, either with or without blue light, under controlled environmental conditions. In the presence of blue light, the mean time required to reach 50% bud burst was reduced by 3.3 days in Betula pendula, 6 days in Alnus glutinosa, and 6.3 days in Quercus robur. This result highlights the potential of the blue region of the solar spectrum to be used as an extra cue that could help plants to regulate their spring phenology, alongside photoperiod and temperature. Understanding how plants combine photoreceptor-mediated cues with other environmental cues such as temperature to control phenology is essential if we are to accurately predict how tree species might respond to climate change.\n\nKey MessageAn LED spectrum containing blue light advanced bud burst in branches of Betula pendula, Alnus glutinosa and Quercus robur compared with a spectrum without blue light in a controlled environment.

plant biology↗