Brilliant and fascinating!

I thought the sentences following your second quotation from the first paper, hypothesizing on the mechanism for kin selection, to be quite interesting:

> This may have been facilitated by the greater mycorrhizal colonization of kin than stranger seedlings (Asay 2013), creating a stronger sink in the MN, an effect also noted in the study by File et al. (2012). The greater colonization of kin seedlings may have arisen from complimentary genetics of the fungal genet and tree genotype (e.g. Rosado et al. 1994a, b). [...]although the mechanism through which the MN elicits the behavior response remains to be resolved.

This genetic mechanism makes sense to me.

The first paper talks about many rich, complex relationships. Two topics I thought were very interesting:

> A fungus can express a mutualism with one plant, while simultaneously exploiting a different plant. Mycoheterotrophic plants are perhaps the most extreme example of this type of exploitation, where a plant acquires all of its carbon by parasitizing fungi through the MN (e.g. Leake 1994; Massicotte et al. 2012). These plants link into the MN of a nearby tree and siphon off photosynthate, enabling them to survive and grow. Importantly this reveals the existence of a mechanism by which plants can acquire nutritional levels of carbon from mycorrhizal fungi. The fitness of all participants in this scenario is increased by the existence of the MN: (i) the mycorrhizal fungus acquires carbon from the tree (or multiple trees) and may use the mycoheterotroph as the staging ground for long-distance exploration and colonization, (ii) the mycoheterotroph acquires carbon from the fungus and (iii) the tree gains access to a wider pool of soil resources, and potentially connection to other trees facilitating the detection of defence signals.

> There is evidence for both tit-for-tat and reciprocal altruism in MNs in forests, both which would be resistant to cheaters (i.e. individuals that benefit without reciprocating). Tit-for-tat, distinct from mutualisms, is evident in bidirectional transfer between paper birch and Douglas-fir (Simard et al. 1997a, b; Philip et al. 2010) and between unrelated Douglas-fir (Teste et al. 2010). This cooperative bidirectional exchange occurs over a period of a few days and appears to be related to the behaviour and possibly fitness of the individuals involved in the network. However, reciprocal altruism, or repeated prisoners dilemma, occurs over longer time periods, and this explanation is more congruent with the highly variable disturbances and hiatus in forests. There is some evidence for reciprocal altruism through the switches in the direction of net carbon transfer between paper birch and Douglas-fir (Philip 2006) or maple and trout lily seedlings (Lerat et al. 2002) in response to differential changes in plant phenology over a period of several months.

Your second paper on kin selection appears to be mainly theoretical on the topic of competition theory, not an observational study of plants or fungi. It makes weak conclusions like "It is reasonable to hypothesize that traits expressed only in the presence of strangers may indicate competition or selfishness, while traits expressed in the presence of kin may indicate cooperation or altruism (Murphy & Dudley 2009; File et al. 2012)" and "It is too soon to know if plant kin recognition responses will demonstrate the breadth that has been found for kin selection in animal behaviour."

> But selection can also take place on the whole plant community.

No doubt.