The colonization of terrestrial environments by rooted vascular plants had far-reaching impacts on the Earth system. However, the belowground structures of early vascular plants are rarely documented, and thus the plant−soil interactions in early terrestrial ecosystems are poorly understood. Here we report the earliest rooted paleosols (fossil soils) in Asia from Early Devonian deposits of Yunnan, China. Plant traces are extensive within the soil and occur as complex network-like structures, which are interpreted as representing long-lived, belowground rhizomes of the basal lycopsid Drepanophycus. The rhizomes produced large clones and helped the plant survive frequent sediment burial in well-drained soils within a seasonal wet−dry climate zone. Rhizome networks contributed to the accumulation and pedogenesis of floodplain sediments and increased the soil stabilizing effects of early plants. Predating the appearance of trees with deep roots in the Middle Devonian, plant rhizomes have long functioned in the belowground soil ecosystem. This study presents strong, direct evidence for plant−soil interactions at an early stage of vascular plant radiation. Soil stabilization by complex rhizome systems was apparently widespread, and contributed to landscape modification at an earlier time than had been appreciated.
The earliest known ovules in the Late Devonian (Famennian) are borne terminally on fertile branches and are typically enclosed in a cupule. Among these ovules are some that have terete integumentary lobes with little or no fusion. Here, we report a new taxon,
Latisemenia longshania
, from the Famennian of South China, which bears cupulate ovules that are terminal as well as opposite on the fertile axis. Each ovule has four broad integumentary lobes, which are extensively fused to each other and also to the nucellus. The cupule is uniovulate, and the five flattened cupule segments of each terminal ovule are elongate cuneate and shorter than the ovule. Associated but not attached pinnules are laminate and
Sphenopteris
-like, with an entire or lobate margin.
Latisemenia
is the earliest known plant with ovules borne on the side of the fertile axis and may foreshadow the diverse ovule arrangements found among younger seed plant lineages that emerge in the Carboniferous. Following the telome theory,
Latisemenia
demonstrates derived features in both ovules and cupules, and the shape and fusion of integumentary lobes suggest effective pollination and protection to the nucellus. Along with other recent discoveries from China,
Latisemenia
extends the palaeogeographic range of the earliest seed plants.
Plant diversity in agro-ecosystems is an important component of global biodiversity. However, wild plant diversity in agro-ecosystems is influenced by herbicide use. We reviewed recent studies on the impacts of herbicides on wild plant diversity in agro-ecosystems and the underlying mechanisms. It is found that herbicide application (i) decreases the number of plants that are sensitive to herbicides; (ii) increases the number of plants that are resistant to herbicides; (iii) changes species composition; and (iv) decreases genetic diversity and species diversity of wild plants in agro-ecosystems. Herbicide impacts simplify plant functional groups and hence add instability to communities. The underlying mechanism is that herbicides kill plants or change plant metabolism, resistance, reproduction and the habitat of plants. Furthermore, herbicides, human activities, and environmental factors have interactions. The impacts of herbicides on plants are plant-specific and the responses of various species or communities to the herbicides are also different. At present, the use of herbicides is increasing rapidly in agricultural production in China. We therefore suggest that more studies are needed on the impact of herbicides on wild plants and the underlying mechanisms, and the historical performances of herbicides use should be studied using long-term monitoring of wild plant changes carried out in China's agro-ecosystems. Studies on policies and laws related to the use of herbicides also need to be strengthened, whicn can help to improve conservation of biodiversity in agro-ecosystem of China.
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