Phytolith‐associated potassium in fern: characterization, dissolution properties and implications for slash‐and‐burn agriculture

• Published in: Soil use and management Vol. 34; no. 1; pp. 28 - 36
• Main Authors: Tran, C. T., Mai, N. T., Nguyen, V. T., Nguyen, H. X., Meharg, A., Carey, M., Dultz, S., Marone, F., Cichy, S. B., Nguyen, M. N., Aitkenhead, Matt
• Format: Journal Article
• Language: English
• Published: Bedfordshire Wiley Subscription Services, Inc 01.03.2018
• Subjects: Ash; Ashes; Burning; Crops; Dicranopteris linearis; Dissolution; fern; Ferns; Heat treatment; Microscopy; Organic matter; phytolith; Plant cells; Potassium; Shifting cultivation; Silica; Silicon dioxide; Tropical environment; Tropical environments
• ISSN: 0266-0032; 1475-2743
• DOI: 10.1111/sum.12409

In recent time, phytoliths (silicon deposition between plant cells) have been recognized as an important nutrient source for crops. The work presented here aims at highlighting the potential of phytolith‐occluded K pool in ferns. Dicranopteris linearis (D. linearis) is a common fern in the humid subtropical and tropical regions. Burning of the fern D. linearis is, in slash‐and‐burn regions, a common practice to prepare the soil before planting. We characterised the phytolith‐rich ash derived from the fern D. linearis and phytolith‐associated potassium (K) (phytK), using X‐ray tomographic microscopy in combination with kinetic batch experiments. D. linearis contains up to 3.9 g K/kg d.wt, including K subcompartmented in phytoliths. X‐ray tomographic microscopy visualized an interembedding structure between organic matter and silica, particularly in leaves. Corelease of K and Si observed in the batch experiments confirmed that the dissolution of ash phytoliths is one of major factors controlling K release. Under heat treatment, a part of the K is made available, while the remainder entrapped into phytoliths (ca. 2.0–3.3%) is unavailable until the phytoliths are dissolved. By enhanced removal of organic phases, or forming more stable silica phases, heat treatment changes dissolution properties of the phytoliths, affecting K release for crops and soils. The maximum releases of soluble K and Si were observed for the phytoliths treated at 500–800 °C. For quantitative approaches for the K provision of plants from the soil phytK pool in soils, factors regulating phytolith dissolution rate have to be considered.