The value of wet leaves Dawson, Todd E.; Goldsmith, Gregory R.
The New phytologist,
September 2018, Letnik:
219, Številka:
4
Journal Article
Recenzirano
Odprti dostop
An often-overlooked feature of all plants is that their leaf surfaces are wet for significant periods over their lifetimes. Leaf wetting has a number of direct and indirect effects on plant function ...from the scale of the leaf to that of the ecosystem. The costs of leaf wetting for plant function, such as the growth of pathogens and the leaching of nutrients, have long been recognized. However, an emerging body of research has also begun to demonstrate some very clear benefits. For instance, leaf wetting can improve plant–water relations and lead to increased photosynthesis. Leaf wetting may also lead to synergistic effects on plant function, such as when leaf water potential improvements lead to enhanced growth that does not occur when plant leaves are dry. We identify important reasons why leaf wetting can be critical for plant sciences to not only acknowledge, but also directly address, in future research. To do so, we provide a framework for the consideration of the relative balance of the various costs and benefits resulting from leaf wetting, as well as how this balance may be expected to change given projected scenarios of global climate change in the future.
Climate, physical landscapes, and biota interact to generate heterogeneous hydrologic conditions in space and over time, which are reflected in spatial patterns of species distributions. As these ...species distributions respond to rapid climate change, microrefugia may support local species persistence in the face of deteriorating climatic suitability. Recent focus on temperature as a determinant of microrefugia insufficiently accounts for the importance of hydrologic processes and changing water availability with changing climate. Where water scarcity is a major limitation now or under future climates, hydrologic microrefugia are likely to prove essential for species persistence, particularly for sessile species and plants. Zones of high relative water availability – mesic microenvironments – are generated by a wide array of hydrologic processes, and may be loosely coupled to climatic processes and therefore buffered from climate change. Here, we review the mechanisms that generate mesic microenvironments and their likely robustness in the face of climate change. We argue that mesic microenvironments will act as species‐specific refugia only if the nature and space/time variability in water availability are compatible with the ecological requirements of a target species. We illustrate this argument with case studies drawn from California oak woodland ecosystems. We posit that identification of hydrologic refugia could form a cornerstone of climate‐cognizant conservation strategies, but that this would require improved understanding of climate change effects on key hydrologic processes, including frequently cryptic processes such as groundwater flow.
In warming, drying climates, locally wet sites could form hydrologic microrefugia in which species could persist even as the surrounding landscape becomes unsuitable habitat. A wide variety of physical processes could form locally wet sites, which, if they meet physiological and community‐interaction requirements, could act as microrefugia. Identifying these sites could strengthen climate‐cognizant conservation strategies, but requires improved understanding of hard‐to‐observe hydrologic processes such as groundwater flow.
Significance Recent reports of widespread drought-induced plant die-back have enhanced the need to understand variation in plant hydraulic strategies and to determine which species are susceptible to ...drought-induced mortality. Finding meaningful ways to describe the many different types of responses plants might demonstrate in biodiverse regions can be extremely challenging. Here, we present the architecture in which functional traits can be incorporated into a known hydraulic framework to provide additional insight into the range of hydraulic strategies present in diverse communities. Merging stomatal regulation strategies that represent an index of water use behavior with xylem hydraulic strategies that represent water transport and vulnerability to water deficit behavior facilitates a more comprehensive framework to characterize plant response to drought.
Attempts to understand mechanisms underlying plant mortality during drought have led to the emergence of a hydraulic framework describing distinct hydraulic strategies among coexisting species. This framework distinguishes species that rapidly decrease stomatal conductance (g ₛ), thereby maintaining high water potential (P ₓ; isohydric), from those species that maintain relatively high g ₛ at low P ₓ, thereby maintaining carbon assimilation, albeit at the cost of loss of hydraulic conductivity (anisohydric). This framework is yet to be tested in biodiverse communities, potentially due to a lack of standardized reference values upon which hydraulic strategies can be defined. We developed a system of quantifying hydraulic strategy using indices from vulnerability curves and stomatal dehydration response curves and tested it in a speciose community from South Africa’s Cape Floristic Region. Degree of stomatal regulation over cavitation was defined as the margin between P ₓ at stomatal closure (P g₁₂) and P ₓ at 50% loss of conductivity. To assess relationships between hydraulic strategy and mortality mechanisms, we developed proxies for carbon limitation and hydraulic failure using time since P g₁₂ and loss of conductivity at minimum seasonal P ₓ, respectively. Our approach captured continuous variation along an isohydry/anisohydry axis and showed that this variation was linearly related to xylem safety margin. Degree of isohydry/anisohydry was associated with contrasting predictions for mortality during drought. Merging stomatal regulation strategies that represent an index of water use behavior with xylem vulnerability facilitates a more comprehensive framework with which to characterize plant response to drought, thus opening up an avenue for predicting the response of diverse communities to future droughts.
Stable water isotopes are widely used in ecohydrology to trace the transport,
storage, and mixing of water on its journey through landscapes and
ecosystems. Evaporation leaves a characteristic ...signature on the isotopic
composition of the water that is left behind, such that in dual-isotope
space, evaporated waters plot below the local meteoric water line (LMWL) that
characterizes precipitation. Soil and xylem water samples can often plot
below the LMWL as well, suggesting that they have also been influenced by
evaporation. These soil and xylem water samples frequently plot along linear
trends in dual-isotope space. These trend lines are often termed “evaporation
lines” and their intersection with the LMWL is often interpreted as the
isotopic composition of the precipitation source water. Here we use numerical
experiments based on established isotope fractionation theory to show that
these trend lines are often by-products of the seasonality in evaporative
fractionation and in the isotopic composition of precipitation. Thus, they
are often not true evaporation lines, and, if interpreted as such, can yield
highly biased estimates of the isotopic composition of the source water.
The broad utility of native chemical ligation (NCL) in protein synthesis has fostered a search for methods that enable the efficient synthesis of C-terminal peptide-thioesters, key intermediates in ...NCL. We have developed an N-acylurea (Nbz) approach for the synthesis of thioester peptide precursors that efficiently undergo thiol exchange yielding thioester peptides and subsequently NCL reaction. However, the synthesis of some glycine-rich sequences revealed limitations, such as diacylated products that can not be converted into N-acylurea peptides. Here, we introduce a new N-acylurea linker bearing an o-amino(methyl)aniline (MeDbz) moiety that enables in a more robust peptide chain assembly. The generality of the approach is illustrated by the synthesis of a pentaglycine sequence under different coupling conditions including microwave heating at coupling temperatures up to 90 C, affording the unique and desired N-acyl-N′-methylacylurea (MeNbz) product. Further extension of the method allowed the synthesis of all 20 natural amino acids and their NCL reactions. The kinetic analysis of the ligations using model peptides shows the MeNbz peptide rapidly converts to arylthioesters that are efficient at NCL. Finally, we show that the new MeDbz linker can be applied to the synthesis of cysteine-rich proteins such the cyclotides Kalata B1 and MCoTI-II through a one cyclization/folding step in the ligation/folding buffer.
Intramolecular activation of C‐terminal peptides: Mildly activated N‐acylurea peptides are readily formed on the solid support following chain assembly, avoiding over‐activation of the C‐terminus. ...The utility of these peptides is demonstrated by the native chemical ligation of unprotected peptides (see scheme; R=amino acid side chain).
Use of the stable isotopes of water (δD, δ18O) to determine vegetative water sources, runoff paths, and residence times generally assumes that, other than shallow evaporative enrichment, the isotopic ...composition of precipitation is conserved as it travels through the subsurface to the stream channel. Here we follow rainfall through a thick (up to 25m) vadose zone of soil, saprolite, and weathered bedrock mostly composed of argillite, and underlying a steep (32°) forested hillslope. We discover a persistent structured heterogeneity of water isotopes inside the hillslope. Summer dry season causes evaporative enrichment of the soil, but not in the saprolite and weathered bedrock. In winter, the mobile water, generated by successive rainstorms with widely varying isotopic composition, mixes in the vadose zone, elevating soil and rock moisture content, and eventually recharging the groundwater with isotopically invariant water similar to the seasonally averaged rainfall. Yet throughout the winter the less mobile winter soil and rock moisture remains relatively light, and water extracted from the interior of argillite lies well to the left of the local meteoric water line. This persistently light composition of soil and rock moisture and the deviation from average meteoric values suggest that subsurface fractionation, or the inheritance of paleo‐meteoric rock moisture associated with rock uplift may lead to large enduring isotopic differences between high and low mobility water. These differences suggest that the use of water isotopes as tracers must consider the possibility of subsurface isotopic evolution and the influence of exchange with more tightly held water.
Key Points:
Material properties in the subsurface impart an isotopic “fingerprint” on their waters
A structured heterogeneity of water isotopes persists in the subsurface of the critical zone
We sample deeply and frequently to characterize water isotopes for ecohydrologic tracers
• Mediterranean‐type ecosystems contain 20% of all vascular plant diversity on Earth and have been identified as being particularly threatened by future increases in drought. Of particular concern is ...the Cape Floral Region of South Africa, a global biodiversity hotspot, yet there are limited experimental data to validate predicted impacts on the flora. In a field rainout experiment, we tested whether rooting depth and degree of isohydry or anisohydry could aid in the functional classification of drought responses across diverse growth forms. • We imposed a 6‐month summer drought, for 2 yr, in a mountain fynbos shrubland. We monitored a suite of parameters, from physiological traits to morphological outcomes, in seven species comprising the three dominant growth forms (deep‐rooted proteoid shrubs, shallow‐rooted ericoid shrubs and graminoid restioids). • There was considerable variation in drought response both between and within the growth forms. The shallow‐rooted, anisohydric ericoid shrubs all suffered considerable reductions in growth and flowering and increased mortality. By contrast, the shallow‐rooted, isohydric restioids and deep‐rooted, isohydric proteoid shrubs were largely unaffected by the drought. • Rooting depth and degree of iso/anisohydry allow a first‐order functional classification of drought response pathways in this flora. Consideration of additional traits would further refine this approach.
Macrocyclization is a broadly applied approach for overcoming the intrinsically disordered nature of linear peptides. Herein, it is shown that dichloroacetone (DCA) enhances helical secondary ...structures when introduced between peptide nucleophiles, such as thiols, to yield an acetone‐linked bridge (ACE). Aside from stabilizing helical structures, the ketone moiety embedded in the linker can be modified with diverse molecular tags by oxime ligation. Insights into the structure of the tether were obtained through co‐crystallization of a constrained S‐peptide in complex with RNAse S. The scope of the acetone‐linked peptides was further explored through the generation of N‐terminus to side chain macrocycles and a new approach for generating fused macrocycles (bicycles). Together, these studies suggest that acetone linking is generally applicable to peptide macrocycles with a specific utility in the synthesis of stabilized helices that incorporate functional tags.
Macrocyclizations are broadly applied for overcoming the intrinsically disordered nature of linear peptides. Dichloroacetone (DCA) enhances helical secondary structures when introduced between peptide nucleophiles, such as thiols, to yield an acetone‐linked bridge. The ketone moiety embedded in the linker can be modified with diverse molecular tags by oxime ligation.
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