A green roof is a vegetated roof or deck designed to provide urban greening for buildings, people, or the environment. Made popular across Europe over the past few decades, green roofs are now ...becoming more familiar to North Americans as some cities have built green roof pilot projects and adopted incentives for using green roofs or even require their use. Green roof standards and guidelines are also emerging to be used for governance and project specification. Although much is known about the application of green roofs across Europe, much less is known about their application across North America's diverse ecological regions. When considering the many decisions required in applying green roof technology to a specific place, there are few choices more critical to their success than the selection of appropriate vegetation. We conducted a review of green roof research to investigate what is known about the application of plants on green roofs across North America and their ecological implications. Results indicate that investigation sites across ecoregions begin to reveal differences in plant survival. Although ecological investigations are limited, their results show improved plant performance and ecological services with diverse green roofs. We conclude that as green roofs continue to become regulated and adopted in policy, further development of standards and guidelines is needed. To date, there is no common ground for reporting of green roof research, and we make recommendations for facilitating such efforts for improved research, policy development and their management across North America's diverse ecological regions.
•Wet reference temperature was well-predicted based on temperature of a dry surface.•Wet and dry leaf temperatures were linearly related to the temperature of green paper.•CWSI could be calculated by ...modeling the wet and dry leaf temperatures.•The same reference can be used both in the sun and shade and for different species.
Leaf temperature (TL) is tightly coupled with the rate of transpirational water loss from the leaf. The temperatures of wet and dry reference leaf surfaces (Twet and Tdry, respectively) are commonly used to normalize temperature measurements for current environmental conditions and then calculate a crop water stress index (CWSI).
Since it is often impractical to directly measure Tdry and Twet, the goals of this work were to: i) determine a suitable artificial reference surface that makes application of the CWSI faster and easier in the field, ii) develop a model for Tdry and Twet based on the reference surface temperature that allows for calculation of standard CWSIs, iii) test the technique for a range of weather conditions and tree species, and iv) analyze the sensitivity of these two models to Tdry and Twet, and their impact on the estimation of four different CWSIs.
Our results showed that both Tdry and Twet are linearly related to the thermal temperature of green paper across a wide range of environmental conditions. Although there was a significant effect of the light conditions on Tdry and Twet, the same models could be used in both the sun and shade to relate Tdry and Twet to Tref. Moreover, results indicated that a new CWSI dependent only on TL and Twet was least sensitive to errors in Twet, but most sensitive to TL.
In recent years, increased awareness of the potential interactions between rising atmospheric
CO2
concentrations (
CO2
) and temperature has illustrated the importance of multifactorial ecosystem ...manipulation experiments for validating Earth System models. To address the urgent need for increased understanding of responses in multifactorial experiments, this article synthesizes how ecosystem productivity and soil processes respond to combined warming and
CO2
manipulation, and compares it with those obtained in single factor
CO2
and temperature manipulation experiments. Across all combined elevated
CO2
and warming experiments, biomass production and soil respiration were typically enhanced. Responses to the combined treatment were more similar to those in the
CO2
‐only treatment than to those in the warming‐only treatment. In contrast to warming‐only experiments, both the combined and the
CO2
‐only treatments elicited larger stimulation of fine root biomass than of aboveground biomass, consistently stimulated soil respiration, and decreased foliar nitrogen (N) concentration. Nonetheless, mineral N availability declined less in the combined treatment than in the
CO2
‐only treatment, possibly due to the warming‐induced acceleration of decomposition, implying that progressive nitrogen limitation (PNL) may not occur as commonly as anticipated from single factor
CO2
treatment studies. Responses of total plant biomass, especially of aboveground biomass, revealed antagonistic interactions between elevated
CO2
and warming, i.e. the response to the combined treatment was usually less‐than‐additive. This implies that productivity projections might be overestimated when models are parameterized based on single factor responses. Our results highlight the need for more (and especially more long‐term) multifactor manipulation experiments. Because single factor
CO2
responses often dominated over warming responses in the combined treatments, our results also suggest that projected responses to future global warming in Earth System models should not be parameterized using single factor warming experiments.
A greenhouse study was conducted to evaluate the growth and development of poinsettia ‘Prestige Red’ (Euphorbia pulcherrima) grown in a commercial peat-based potting mix (Sunshine Mix #1) amended ...with biochar at 0%, 20%, 40%, 60%, 80%, or 100% (by volume) at four different fertigation regimes: F1: 100 to 200 mg·L−1 nitrogen (N), F2: 200 to 300 mg·L−1 N (control), F3: 300 to 400 mg·L−1 N, or F4: 400 to 500 mg·L−1 N. The experiment was a two-factor factorial design with 10 replications for each combination of biochar by fertigation. As the percentage of biochar increased, root substrate pore space and bulk density increased, while container capacity decreased. Root rot and red bract necrosis only occurred in F4 combined with 100% biochar. Plants grown in 40% biochar had a similar growth and development to those in 0% biochar. Up to 80% biochar, plants exhibited no significant change, except in terms of dry weight, which decreased at higher biochar percentages (60% and 80%). In summary, at a fertigation rate of 100 mg·L−1 N to 400 mg·L−1 N, up to 80% biochar could be used as an amendment to peat-based root substrate with acceptable growth reduction and no changes in quality.
California signed the Sustainable Groundwater Management Act (SGMA) into law in 2014. SGMA requires groundwater-dependent regions to halt overdraft and develop plans to reach an annual balance of ...pumping and recharge. Groundwater aquifers can be recharged by flooding agricultural fields when fallow, but this has not been an option for perennial crops such as fruit and nut trees. While flooding these crops might be possible during the dormant season, it is not known what impact flooding might have on tree-root systems, health and yield. We followed root production, tree water status and yield in two almond orchards in Northern California for 2 years to test the impact of applying captured winter water runoff for groundwater recharge purposes on tree performance. Results showed that more than 90% of the water applied to sandy soil and 80% of the water applied to loamy soil percolated past the root zones, with no measured adverse effects on tree water status, canopy development or yield. Groundwater recharge did not negatively affect new root production and tended to extend root lifespan. Based upon these data, applying additional water in late December and January is not likely to have negative impacts on almond orchards in moderately drained to well-drained soils.
•Drought significantly reduced plant water potential, biomass accumulation, and gas exchange, while increasing stomatal limitation.•Neither stem water potential nor gas exchange were significantly ...altered by inoculation. We found that inoculation did slightly elevate leaf nand P concentrations in the low water treatments, although not consistently across years.•There were no interactive effects between drought and mycorrhizal inoculation on growth or gas exchange parameters in either year.•Contrary to expectations we did not find substantially greater benefits from mycorrhizal inoculation in drought stressed treated plants. We conclude that for almond trees, the potential for mycorrhizal incculation to alleviate drought stress in containerized trees is minimal.
Very little is known about potential benefits of using AM inoculation as a tool to alleviate drought stress of trees grown under nursery conditions. There is some evidence that benefits of mycorrhiza on gas exchange parameters and growth of trees are proportionally greater when trees are subjected to drought stress. We hypothesized that inoculation with mycorrhiza would increase growth, nutrition, stem water potential and gas exchange of containerized almond (Prunus dulcis (Mill.) D.A. Webb) when young trees are grown under low water availability.
In the spring of 2015 and 2016, forty containerized almond trees (Nonpareil scion grafted on Hansen 536, a peach/almond hybrid rootstock) were either inoculated or not with a commercially available arbuscular mycorrhizal inoculum and kept well-watered for 60 days in 2015 and 54 days in 2016, after which half of the plants were exposed to gradually reduced water availability over 38 days in 2015 and 61 days in 2016. Measurements included growth metrics, stem water potential, stomatal density, leaf NPK concentration, light saturated photosynthesis, and parameters calculated from CO2 response curves (Vcmax, J, TPU, Rd, gm, and stomatal limitation).The low-water treatment decreased stem water potential and reduced trunk diameter growth, light saturated photosynthesis (A), stomatal conductance (gs), Vcmax, J, TPU, gm, specific root length, leaf N and K concentration and total leaf N, P, and K content. Inoculation decreased root mass, increased leaf mass fraction, and decreased root mass fraction in 2015, but not in 2016. Neither stem water potential nor gas exchange were significantly altered by inoculation. Inoculation decreased leaf stomatal density, and slightly elevated leaf N and P concentrations in the low water treatments, although not consistently across years. Contrary to expectations we did not find substantially greater benefits from mycorrhizal inoculation in young drought stressed almond trees and conclude that the potential for mycorrhizal inoculant to alleviate drought stress in containerized trees is minimal.
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Coupled surface-atmosphere models are being used with increased frequency to make predictions of tropospheric chemistry on a 'future' earth characterized by a warmer climate and elevated atmospheric ...CO2 concentration. One of the key inputs to these models is the emission of isoprene from forest ecosystems. Most models in current use rely on a scheme by which global change is coupled to changes in terrestrial net primary productivity (NPP) which, in turn, is coupled to changes in the magnitude of isoprene emissions. In this study, we conducted measurements of isoprene emissions at three prominent global change experiments in the United States. Our results showed that growth in an atmosphere of elevated CO2 inhibited the emission of isoprene at levels that completely compensate for possible increases in emission due to increases in aboveground NPP. Exposure to a prolonged drought caused leaves to increase their isoprene emissions despite reductions in photosynthesis, and presumably NPP. Thus, the current generation of models intended to predict the response of isoprene emission to future global change probably contain large errors. A framework is offered as a foundation for constructing new isoprene emission models based on the responses of leaf biochemistry to future climate change and elevated atmospheric CO2 concentrations.
•Unirrigated green roof trays were installed in a warm and dry Texas climate.•Retention efficiency was 100% for events <7.4mm and declined with increasing event size.•Increased plant species cover ...increased retention efficiency.•Drier green roof substrate provided additional retention benefits for large events.•Finding species that survive on unirrigated roofs will be a major challenge in dry climates.
As green roofs continue to grow in popularity more research will be needed in new ecoregions to support development of policy, regulation, and incentives. Extensive green roofs represent the majority of new construction each year and understanding their performance expectations is critical for regulation. In our experiment we tested the ability of three monocultures of low stature CAM plants (Sedum kamtschaticum, Delosperma cooperi and Talinum calycinum syn. Phemeranthus calycinus) to improve runoff reduction efficiency of un-irrigated modular extensive green roofs exposed to a range of precipitation event sizes in a warm and dry southern US climate. Stormwater runoff data were collected for 15 rainfall events that ranged from a minimum of 4.1mm to a maximum of 102.9mm. An average precipitation event retention efficiency of 78% was recorded. On average, the presence of T. calycinum enhanced retention efficiency by an additional 7.5% compared to unvegetated modules. Substrate volumetric water content affected retention capacity of unvegetated modules only.
•Peanut leaf water potential was lower when intercropped as compared to monoculture.•Watermelon exhibited morphological plasticity in response to competition.•Differences in gas exchange were ...detected only in one of five species.•Water use efficiency was enhanced in dominant crops but reduced in subordinate crops.
Interspecies specific interactions are generally regarded as drivers of plant productivity in multispecies agroecosystems. Complementary use of resource in diverse communities can enhance community productivity through optimal use of plant-available resources and positive interactions such as facilitation can ameliorate high abiotic stress conditions. We studied the effects on physiological response, leaf traits and water use efficiency of a multifunctional species intercropping system consisting of peanut (Arachis hypogaea L.), watermelon Citrullus lanatus (Thunb.) Matsum. & Nakai, okra Abelmoschus esculentus (L.) Moench, cowpea Vigna unguiculata (L.) Walp., and pepper (Capsicum annuum L.) planted alone or in various intercropping combinations in a low fertilizer input system in the peak of summer heat in Texas. Differences in gas exchange measurements were detected only in watermelon in year 2 of the study when okra was the dominant crop. This same year watermelon specific leaf area (SLA) was significantly higher when okra was present in a treatment and particularly in the three and four species combinations, Wpwo and Wpwoc, 27.5 and 31.0m2kg−1, respectively, as compared to watermelon grown in monoculture, strip intercropped with peanut (Spw) and within row intercropped with peanut (Wpw), 20.4, 20.1, and 19.8m2kg−1, respectively. This corresponds with an increase watermelon leaf N concentration and a decrease in leaf C:N ratio in Wpwo and Wpwoc treatments. No differences in d13C composition, a measure of water use efficiency over the leaf lifespan, were detected across cropping system for each species. Water use efficiency based on per plant production (WUEyield) indicated an increase in water use efficiency in dominant crops such as watermelon in 2011 and okra in 2012, but a reduction in WUEyield subordinate crops such as cowpea and pepper both years of the study. Peanut grown in monoculture and strip intercropped with watermelon had significantly lower leaf water potential values in 2012, −2.2 and −2.1MPa, respectively, as compared to intercropping systems increasing in level of integration (Wpw=−1.1,Wpwo=−0.6,Wpwoc=−1.3,Wall=−1.1MPa), indicating peanut benefited from alterations to microclimate and facilitative interactions with companion crops in some intercropping systems through a reduction in plant water stress. The results from this study suggest there may be a benefit to a multifunctional intercropping system in the form of increased food production per unit of water input in dominant crops and reduced water stress for some component species. This is important to producers; showing a method to increase overall crop production without increasing water inputs.
Savanna tree–grass interactions may be particularly sensitive to climate change. Establishment of two tree canopy dominants, post oak (Quercus stellata) and eastern redcedar (Juniperus virginiana), ...grown with the dominant C4 perennial grass (Schizachyrium scoparium) in southern oak savanna of the United States were evaluated under four climatic scenarios for 6 years. Tree–grass interactions were examined with and without warming (+1.5 °C) in combination with a long‐term mean rainfall treatment and a modified rainfall regime that redistributed 40% of summer rainfall to spring and fall, intensifying summer drought. The aim was to determine: (1) the relative growth response of these species, (2) potential shifts in the balance of tree–grass interactions, and (3) the trajectory of juniper encroachment into savannas, under these anticipated climatic conditions. Precipitation redistribution reduced relative growth rate (RGR) of trees grown with grass. Warming increased growth of J. virginiana and strongly reduced Q. stellata survival. Tiller numbers of S. scoparium plants were unaffected by warming, but the number of reproductive tillers was increasingly suppressed by intensified drought each year. Growth rates of J. virginiana and Q. stellata were suppressed by grass presence early, but in subsequent years were higher when grown with grass. Quercus stellata had overall reduced RGR, but enhanced survival when grown with grass, while survival of J. virginiana remained near 100% in all treatments. Once trees surpassed a threshold height of 1.1 m, both tiller number and survival of S. scoparium plants were drastically reduced by the presence of J. virginiana, but not Q. stellata. Juniperus virginiana was the only savanna dominant in which neither survival nor final aboveground mass were adversely affected by the climate scenario of warming and intensified summer drought. These responses indicate that climate warming and altered precipitation patterns will further accelerate juniper encroachment and woody thickening in a warm‐temperate oak savanna.
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