Search

Extensive green roofs substrates should meet a list of physicochemical and biochemical requirements to be used as a basis for plant growth: high water holding capacity, good aeration, low bulk density, and proper drainage are some of them. In recent years, the impact of different organic matter doses and the substrate depth on the subsequent plant growth have been deeply studied. By contrast, there are not many publications about the effect of the inorganic component of these substrates on plant development and C and N sequestration potential by the green roof system, and even more under semi-arid Mediterranean conditions. Four substrates were made by mixing the same compost, at 10% by volume, with different inorganic materials: CsB (compost, silica sand, and crushed bricks; 1:1:8), CB (compost and crushed bricks; 1:9), CSB (compost, clay-loam soil, and crushed bricks; 1:1:8), and CsS (compost, silica sand, and clay-loam soil; 1:1:8). These were placed, a depth of 10 cm, on “cultivation tables” in an experimental farm located in the SE of Spain. Two native species were sown in each substrate: Lotus creticus and Asteriscus maritimus . Physicochemical, nutritional, and biochemical properties of the substrates as well as the plant development were evaluated during a 10-month experiment. The CsB and CSB mixtures had good physicochemical properties (high porosity and acceptable water holding capacity) although the levels of C, N, and humic substances were higher in the soil-containing substrates than in the CB and CsB mixtures. The hydrolytic enzyme activity was also promoted in these mixtures. The plant growth pattern showed differences regarding the inorganic composition of the substrate; L. creticus had superior development in the CsB substrate and A. maritimus was able to grow in all tested substrate mixtures, although its cover was low, being a more versatile candidate to establish a green roof cover. The greatest C and N sequestration potential was achieved by the CsS mixture, reaching 1.06 kg TC m −2 of green roof substrate. Therefore, substrate composition impacts the growth of native plant species as well as the C and N sequestration by the green roof system. [ABSTRACT FROM AUTHOR]

The study of the growth of several Mediterranean endemic plant species in new artificial substrates is becoming necessary for seeking alternatives in green roof design in Mediterranean regions. In this regard, we evaluated the growth of six native species on three different artificial substrates. These species were Silene vulgaris, Silene secundiflora, Crithmum maritimum, Lagurus ovatus, Asteriscus maritimus , and Lotus creticus . A mixture of a green compost with a clay–loam soil (C + Soil), the same compost mixed with expanded clay (C + Clay), and the compost mixed with crushed bricks (C + Bricks) – all in 1:4 volumetric proportions – were the assayed substrates. Physichochemical and biochemical properties were studied in each mixture at the beginning and end of a three-month assay. Besides, the germination and growth of all plant species in each substrate type were evaluated. The mixtures C + Clay and C + Bricks showed greater porosity than C + Soil, leading to a high root: shoot biomass ratio in all species tested. Conversely, the mixture C + Soil possessed better biochemical properties (higher humic substances content and enzyme activity), but they decreased with experimental time. Contrarily, the humic substances and the dehydrogenase activity increased in the most porous mixtures. Regarding plant behaviour, S. vulgaris and L. ovatus showed greater germination and growth than the other species, especially above C + Clay and C + Bricks mixtures. Accordingly, we strongly recommend the use of lightweight and highly porous substrates as the basis for the growing of Mediterranean native herbaceous species, since they specially enhance their root development. The combined use of perennials and annuals species in that kind of substrates could provide a permanent plant cover in a green roof scenario. [ABSTRACT FROM AUTHOR]

Abstract: Light management and species light plasticity are critical factors for proper crop production in nurseries. So, to assess the light necessities of Rhamnus alaternus, which is a promising native evergreen Mediterranean shrub of ornamental and ecological interest, it was exposed to five shade levels (0%, 32%, 48%, 84% and 93%) for one year (0% of shade received annual mean maximum photosynthetic photon flux density [PPFD] of 1293±415μmolm−2 s−1 with a summer mean maximum PPFD of 1541±225μmolm−2 s−1 [mean±s.d.]). The treatments providing 84% and 94% shading produced less compact plants, with greater height and less stem diameter, greater specific leaf area and higher shoot/root index. In general, the shading produced dark green leaves except the 94% treatment, in which the leaves were lighter because the relative chlorophyll content was reduced. Leaf thickness was reduced in all the shading treatments compared with the control. The stomatal density and pore area were reduced with the 84% and 93% shading treatments, as was photosystem II (PSII) efficiency and the leaf soluble sugar content (falling to 60% of the control level); in contrast, non-photochemical quenching increased. The 93% treatment caused irreversible damages in PSII because dark-adapted PSII efficiency was reduced. The results show that solar radiation can be used as a tool to improve plant quality during the nursery period. We conclude that shading screens providing more than 84% shade are not recommendable in terms of photochemical activity, soluble sugar content and overall plant quality. Shading screens of 32% and 48% improve R. alaternus quality in spring and summer, respectively. As regards its interest as an understory species for reforestation programs, we also conclude that this shrub can be adapted to a wide range of shade intensities, although its proper development would be compromised in very strong shading conditions. [Copyright &y& Elsevier]

An early study analysing the effects of competition from Cistus monspeliensis-dominated shrub canopy on Pinus halepensis saplings, both colonising a recently burnt area, has been extended in order to test initial predictions. Inter-specific competition effects on P. halepensis were experimentally analysed by a shrub thinning-out treatment carried out 1 year after fire. The extension of the recorded period confirmed (i) a significant increase in height, and (ii) the lack of variation in density of P. halepensis saplings when the shrub layer was removed. In contrast, the increase in relative growth rate in height (RGRh) and the decrease in mortality recorded during early post-fire stages for treated units did not persist in subsequent years. These two treatment-induced effects disappeared 1 year after the shrub clearing (29 months after fire). It is hypothesised that this time should represent a culminating point in the inter-specific competition established between Cistus and Pinus saplings simultaneously colonising recently disturbed areas and be a critical period for pine sapling survival. After this time, a reduction in relatively short-lived Cistus populations and an increase in P. halepensis abundance should be expected in the community. It is concluded that a shrub-clearing treatment could be recommendable if the initial post-fire pine sapling density is not high enough to successfully face the early critical competitive period. Consequences of early shrub competition on forest productivity during mature phases are also discussed. [Copyright &y& Elsevier]

The viability and seed dormancy of the critically endangered species Astragalus nitidiflorus were tested during eight consecutive years (2006–2013) in order to determine if the high physical seed dormancy described in a previous study is affected by annual or seasonal environmental conditions. Also, the effects of maternal factors – such as fruit position in the inflorescence or seed position in the fruit, the age of the mother plants, and water stress – on seed viability and dormancy were tested. In order to determine the variation in the degree of germinability between years, ripe seeds were harvested each July from 2006 to 2013 and their viability and dormancy were tested. Moreover, in 2013 new seeds were collected to check the effects of the maternal factors mentioned above. A trial with potted plant in greenhouse was performed to corroborate the observed field data about the effect of water stress suffered by the mother plant on seed dormancy. The results show a high variability over the years in the physical dormancy of A. nitidiflorus seeds because maternal environmental factors such as drought or mother plant age influence the proportion of seeds that enter dormancy. This in turn determines the proportion of seed that becomes part of the seed bank each year and also the age structure of the natural population. The conservation programs for this critically endangered species should consider these results to implement measures to prevent the extinction of the species. [ABSTRACT FROM AUTHOR]

The Mar Menor (SE Spain), the largest hypersaline coastal lagoon of the Mediterranean basin, suffers a severe eutrophication crisis due to the nutrients that receives from the Campo de Cartagena watershed, mainly nitrate from intensive agriculture. This paper updates the state of the art in relation with nutrient discharges to the Mar Menor, and summarizes results from different tested Nature-Based Solution (NBS). Specifically, we show i) results from a pilot plant with woodchip bioreactors for nitrate-enriched brine denitrification, and ii) the first results obtained in a pilot plant with bioreactors and constructed wetlands for treatment of agricultural drainage water and leachates, as well as other effluents. Nutrient discharges to the lagoon are highly variable and occur via drainage network, drains, stormwater pipes, direct groundwater discharges from the Quaternary aquifer, and others. For instance, between January 2017 and January 2018 measured daily superficial discharge (floods excluded) ofN-NO 3 − amounted from 119 kg d−1 to 1084 kg d−1. Estimations subsurface discharges ranged 815 to 3836 kg N-NO 3 − d−1 in 2018–2020. Field studies in coastal wetlands (e.g. inflow ≈20–30 mg N-NO 3 − L−1, removal ≈80–90%) and results from pilot plants with bioreactors (e.g. inflow ≈30–40 mg N-NO 3 − L−1, removal ≈90–95%) and constructed wetlands (e.g. inflow ≈30–40 mg N-NO 3 − L−1, removal ≈60–70%), showed the good performance of these systems for nutrient retention. Four strategies are considered for reducing nutrient inputs into the Mar Menor, which include a combination of nature-based solutions and best management practices. (i) Reducing the leaching of nitrate to the aquifer and export of nutrients and sediments following heavy rains by improving fertilization, and irrigation routines, and soil conservation measures in the agricultural fields. (ii) Development of effective and scalable tools for denitrification of nitrate-rich brine produced by on-farm desalination plants. (iii) Capture and treatment of polluted water discharged to the Mar Menor via hydrologic networks, subsurface flow, drainage ditches, and others. (iv) Preservation and restoration of coastal wetlands. Unlabelled Image • Mar Menor receives nutrients, mainly from agricultural discharges. • Coastal wetlands acts as buffers protecting the Mar Menor from nutrient inputs. • Bioreactors and CWs are recommended BMP for treatment of nutrient enriched discharges. • In the Campo de Cartagena BMP should be addressed on a watershed scale. • BMP should address fertilization and irrigation protocols and soil conservation. [ABSTRACT FROM AUTHOR]